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About Google Book Search Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web at |http: //books .google .com/I /^S>v -^ N / C3 r. v>^ ' •V^-^FO^^'i^ V. ir. . ■r> - r ■ ■ • HAND-BOOK TO ATLAS OF HUMAN ANATOMY AND PHYSIOLOGY. RY . WILLIAM TUMEK, M.B.C.S. ENG., l>KMONSTrtATOa OP AWATOMY IN THE UNIVERSITY OF EDlNBURnif. THE ILLUSTRATIONS SELECTED AND ARtlANGED UNDER TIIE SUPERINTENDENCE OF JOHN GOODSIE, P.R.SS.L. & E., FflOFRSaOR OF ANATOMY IN THE UNIVERSITY OF ED1NBUjBO»»:-««. EDINBURGH: \ Price of Atlas and Hand'Bookj S II ! ij W. & A. K. JOHNSTON, 4, ST. ANDREWHS<^IIJLiaf, GEOORAFHERS AND ENGRAVERS TO THE QUEEN. LONDON : E. STANFORD, CHARING CROS8 5 GROOMBRTDGE AND SON, I'ATERNOSTER ROW. DUBLIN : M'GLASHAN AND GILL. MDCCCLVll. Sli KNTEKED AT STATIONEKS' HALL. MUKBAV AND UIBH, PKINTEKS, EI>INin'RGll. CONTENTS OF ATLAS. LIST OF ILLUSTRATIONS. Plate 1, The Bones. Plate 2, The Joints and Ligaments. Plate 3, The Muscles. Plate 4, . , The Heart and Akterieh. Plate 5, The Veins and Lungs. Plate 6 The Organs op DigeMion. Plate 7, Tub Nervous System. Plate 8, Organs of Sense anp Voiok . " • ' ' \ \: V 1-. / TABLE OF GONIEKIS CHAPTEBL Page IiriKODUCTOBT, • . . . 11 Definitions of Anatomy and Physiology , ... 11 Diyisions of the Human Body, . U (General Structure of the Body, . 12 Chemical Composition, • 15 General Functions, 17 CHAPTKK n. Thx Skkt^etok, 18 Greneral Description of Skeleton, 18 Shapes of the Bones, 26 Markings on Bones, 27 Naked Eye, Structure of Bone, 28 Microscopic Structure, . 30 Chemical Composition, . 32 Uses of the Skeleton, 33 CHAPTER m. Jonrrs and Lioamxnts, General Description of the Joints, Kinds of Joints, . Structure of Moveable Joints, • Divisions of the Moveable Joint, Morementa ofJointa, . 34 34 38 38 N2^ TABLE OF CONTENTS. CHAPTER IV • Page The Muscles, ....... 49 General Description of the Mascles, Diyisions of Muscles, > 1 50 53 Naked Eye, Structure of Muscles, Mode of Connection of Muscles, » 54 55 Muscular Action, Miscroscopic Structure of Muscles, Lererage of Muscles, 9 t 9 56 59 59 CHAHTEK V. Gekebal Mechanism of the Frame, 61 CH APTER VI. The Heabt Ain> Abtesies, 66 The Heart, 66 Circulation throi£gh the Heart, . •■ • 70 The Arteries, \ •^ 72 Structure of the Arteries, 76 The Capillaries, . 77 TABLE OF CONTENTS. CHAjexEK vn. F^ ThbYbins, ...,.•< 81 Qeneral Distribution of Veins, ,. « • 81 Stnictare of the Veins, • . • . . 86 Uses of the Valyes, . • . • . 86 MoTement? of the Blood, • • • . 88 CHAPTER Vin. ThbBlooi>, . 90 CHAPTERED Thb Lttkgs and Bespisation, Position of the Lungs, . . • • Structure of the Lungs, , . . • Moyements of Respiration, Changes in the Air and Blood, during Respiration, Diagram of the Circulation, • . • 95 96 96 97 100 102 CHAPTER X. ARDfALHSAT, 108 CHAPTER XL Ths Food, • Kinds of Pood, . Hunger and Tbint, 107 VOL TABLE OP CONTENTS. CHAPTER Xn. r Page Obgans and Pbocess of Digestion, 112 Mastication, . . ' . 112 Deglutition, .... 115 Action of the Stomach, . 116 Action of the Tntestines . 117 The Peritoneum, 118 Changes taking place in the Food in the Alimentaby Canal, 118 Action of the Saliva, . • 119 Action of the Gastric Juice, . . • • 119 Action of the Pancreatic Fluid, . . . 121 Action of the Bile, - 121 Action of'the Intestinal Secretion, . . 123 CHAPTEK Xm. •■ » - .• . rf Absobftion, ..... . 123 Absorption from the Digestive Canal, . . 123 Absorption by the Blood- Vessels, . . 124 • Absorption by the Eactealsj *. 125 Absorption by the Body generally. t 126 CHAPTER XIV. NuTBinON AND SeOBETION, . a • • 129 Nutrition^ • . * 129 Secretion, 132 CHAPTER XV. Genebal Pbopebties of Nebtb Tissue, . Nerve Cells, . * Nerve Fibres, .... 133 134 135 CHAPTER XVI. Cbbebbo-Spinal Nebyous Axis, Spinal Marrow, . Spinal Nerves, . Functions ofSpih&L Cotd and Nerves, 138 138 141 TABLE OF CONTENTS. Nerves of the Medulla Oblongata, The Brain, Cranial Nerres, . Functions of the Cerebellmn, Functions of the Cerebnun, Stmfathbtio Nbbtb, Sbnbai^on, CHAPTEBXVn. C5APTEB XVm. CHAPTEBXrX. The Skin and Common Sensation, Stmctore of the Skin, Tonch or Common Sensation, . The Sweat Glands, CHAPTEB XX The Nails and Haib, The Nails, .... The Hair, .... CHAPTEB XXL The Tongue and the Sense of Taste, CHAPTEB XXn. The Eye-Ball and the Sense of Sight, Accessory Structures of the Eye-Ball, The Eye-Ball, . Passage of the Visual Bays, Adaptation of the Eye to Distance, Action of Light upon the Betina, CHAPTEB XXm. The Ear and the Sense of Hearing, Divisions of the Ear, Function of the External Ear, . Functions of the Tympanum, FnndioiiA o/ the Labyrinth, Page 146 148 150 151 152 155 158 160 160 162 163 165 165 165 169 171 172 174 178 180 181 183 183 187 8 TABLE OF CONTENTS. CHAPTER XXIV. P*ge Thb Nose and thb Sense of Smell, • • 189 General Belations of the Senses, . . • .191 Relations of the Openings into the Pharynx, • . 193 CHAPTER XXV. The Groan of Voice, .... .194 Stntctore of the Larynx, • • • . 194 The Voice, ... ... 196 CHAPTER XXVI. Conclusion, ..••,«.. 198 PEEFACE. As the Anatomical EngraTings, to which these pages are the accompuiying Hand-Book, constitute an attempt to introduce into a general education a new feature, some few words respect- ing their nature and object maj not be out of place. A large number of the most distinguished medical authorities <^ the present day hare testified to the adrantages to be derfyed by including some knowledge of the structure and functions of the Human Bodj under the other elements of a general education. Many of those who hare the management of some of our large schools hare also iigreed in the propriety of teaching the rudi- ments of Anatomy and Physiology in those institutions. With the Tiew of facilitating the teaching and acquiring such information, the present publication has been prepared. The popularising of anatomical knowledge is, howeyer, a task of considerable difSculty, for, from the yery nature of the sub- ject, the yarious parts figured and described can of necessity only be seen and handled by the professional and scientific student. Drawings, howeyer accurately they may be executed, and descriptions, howeyer clearly they may be written, both fail to giye BO deSnite an impressioiv as 'W0\il4. \i^ ^^x^^Ns^ "^si. 10 PREFACE. ocnlar demonstration. This necessarily interferes, to a great extent, with the clear conception by the pupil of the parts that the teacher may be describing. It would not be possible, in a work of this kind, to enter minutely into the functions, or to describe in detail the different structures and organs, of the human frame. Those desiring such information may obtain it by referring to the yarious larger works on this subject. It is my intention here only to describe and illustrate the leading principles on which the human body is constructed, and it is with this object that the following ex- amples, as more especially fitted for such illustration, have been selected. The writer must acknowledge his obligations to Professor Goodsir for much yaluable advice, given at various times during the preparation of the work. He has also to thank the artists for the care and attention bestowed upon the preparation of the drawings, many of which are original, the rest being selected from various Anatomical Works. WILLIAM TURNER. COLLBGB OF EdINBTTBGH, August 1857. HUMAN ANATOMY AND PHYSIOLOGY. PART PIEST. CHAPTER I. INTKODUCTOKY. Anatomy, in its most extended sense, signifies a knowledge of the structure or formation of all living beings. Physiology treats of the functions that are performed by living beings, and by the different organs composing them. It is intended in the following pages to explain some of the leadmg points connected with the Anatomy and Physiology of Man. The Human Body is divided into three parts — ^the Head and Neck, Trunk, and Extremities. The head is the sunmiit of the body ; it contains the brain, the organs of sense, and the face, the latter presenting the orifices of the nose and mouth. The neck is the elongated part connect- ing the head to the trunk ; it contains the gullet and windpipe. The trunk consists of two parts ; an upper, called the chest (thorax), containing the heart and lungs — ^the organs of circula- tioh and respiration ; and a lower, called the belly (abdomen), containing the stomach, liver, etc. — ^the organs of digestion. The extremities are, as it were, appendages of the trunk, the two upper ones being named the arms, the two lower the legs. The whole of the outer surface of the bod?j \^ ^ss^^'^Xfc^V^ y highly sensitive protecting structure, ttie ^m\ \k^\vft»30cL ^ss^ssssSss."^ 12 INTRCmnOTOBT. placeO a layer of fat, varying in ita thickness with the Btoutnesa of the individual. These differeDt parts cover the bones, the organs of support ; the muscles, the organs of motion ; the blood-vessels, the tnbea that carry the nutritive fluid ; tlie nerves, the cords that convey the force that indaces sensation and motion ; together with the wails and contents of the cavities of the head, chest, and abdomen. Oeneial Structnie of the Body, — The various structures existing in and composing the human body, may be primarily divided into two great classes. Fluids and Solids, Of the fluids, the most generally diffused is the blood, wliich ia conveyed throughout the entire system along a somewhat com- plex arrangement of tubes. Another fluid existing also pretty ge- nerally, though in much less quantity than the blood, is the lymph. As the blood flows through different parts of the body, cer- tain flnida are separated irom it, whicli, under, the uanie of secretions, fulfil important purposes in the animal economy. Amongst the most remarkable of these are the bile, urine, sweat, and saliva. The animal solids present every shade and variety of density and hardness. The teeth and bones are of a dense, firm, ivory- like texture ; the cartilage is of a softer and more elastic nature ; the muscles are still softer and less firm ; whilst those great nervous masses, the brain and spinal cord, may be readily broken down by the fingers. Not merely do the diffe- rent parts vary greatly in their density, but they present at the same time considerable differences of colour, — every gradation of tint, from the brilliant wliite appearance of the teeth, through the slightly yellowish colour of bone, to the deep reddish brown hue of the muscles. These variations m the colour are doe, to a great extent, though not entirely, to the amount of blood that is contained by the tissue. Certain elementary structures, closely resembling each other in appearance, may be observed in many of the solid tissues. Tie most abundant and generally diffused of these elementary INTBODUCTOBT. 13 particles are the minnte bodies called Cells. These are in every instance so extremely small, that they can only be detected by the aid of a powerful microscope. They all present certain characters in common, having more or less of a bladder-like ap- pearance. At some period or other of their existence, they all possess a distinct wall, which separates the contents of one cell from those adjoining it. These contents are generally fluid, which differ considerably in their nature in the cells found in the different tissues ; but all the cells agree in this respect, that, together with the fluid contained in them, they possess a small solid particle called a nucleus. The nuclei do not always exist in cells, but are often found lying distinct and separate from them amongst the various tissues. The cells vary much in shape. Examples of the different kinds are furnished in several of the Plates, as in Plate 4, Pig. 7, the globules of the blood; Plate 5, Pig. 6, ciliated epithelium cells ; in Plate 6, Pig. 6 and 9, cells of the stomach and liver ; in Plate 7, Fig. 2. nerve-cells. All the tissues, in their primary state, are probably composed to a gr6at extent of these particles. As they grow older, how- ever, certain changes take place in many of them, which result in the disappearance of the cells, or their metamorphosis into other structures, so that the original cellular nature of the tissue be- comes lost or obscured. These changes are especially seen in those tissues in which the functions performed are not very active. In all the structures, however, such as the glands, where the pro- cesses are carried on with great activity, the cells are very nu- merous. Tissues having more or less of a fibrous character, are also extensively diffused throughout the system. One of the most generally present is the tissue especially called fibrous, figured in Plate 2, Pig. 2, the Ligaments. The yellow or elastic fibre, Plate 4, Pig. 5, the Arteries affords another example. Muscular fibre, Plate 3, Pig. 3, and Nerve fibre, Plate 7, Pi^. 2^ «s«^ ^S&io^ instances of Sbrons structures. AIL tlii^e, i\!i3cLQ\\.^ '^o^^^'esss^^ ' 14 INTKODUCTOBT. fibrous character, yet differ, however, materially in their struc- ture from each other. They cannot be regarded either as so elementary in their nature as the cells, and they are probably ^ formed by the elongation and alternation of cells or their nucleL Certain membranes, possessing to some extent corresponding characters, are also to be observed in different parts of the body. Of these the most important are the Mucous and Serous mem- branes. The mucous membranes are found lining all those cavities of the body which open on to the surface. The best marked of these are the membranes lining the cavities of the mouth and nose. These are prolonged on the one hand down the windpipe into the lungs ; and, on the other, down the gullet into the sto- mach, and along the whole length of the intes'tinal canal, to its lower extremity. They secrete a small quantity of a viscid tena- cious fluid called mucus, which keeps their surfaces continually moist. Along the passages lined by these membranes, at certain intervals, materials proceed to or from the organs to which the passages lead. Thus, air is conveyed to the lungs by the wind- pipe, and food passes to the stomach by the gullet. The mucus moistening the surface of the membrane protects it from injury during the passage of any substance along it, whilst, at the same time, it greatly facilitates the passage of any solid material. The serous membranes, on the other hand, do not communicate with the surface. They form, as it were, closed cavities. They are placed within the great cavities of the body, and surround certain of the organs contained therein. They are found where- ever an organ, in the performance of its function, has to move in its position. Their surfaces are consequently smooth, and mois- tened with a small quantity of fluid, in order to facilitate this movement. Of these membranes, the most important are the pleurse, which invest the lungs ; the pericardium, which invests the heart, and the peritoneum, which surrounds the stomach, intestines, and certain other organs contained in the cavity of the nrrBODUCTOKY. 15 Closely allied to the serons are the synovial membranes, which surround the ends, of the bones that enter into the forma- tion of the joints. The fluid secreted by these membranes lubricates the surfaces which move upon each other. Chemical Composition of the Body. — Diverse as these parts appear in their colour, texture and other physical properties, yet, when examined by the aid of chemistry, they are found to present many elements in common. Of the numerous elements which the chemist has detected in the various objects of nature, comparatively only a few appear to be necessary to the formation of the animal body. Of these the most abundant are the elements, oxygen, hydro- gen, nitrogen and carbon, which, from their general diffusion throughout the whole organized world, have been termed the organic elements. By the organized world is meant all those structures, whether animal or vegetable, which possess or have possessed life. Certain other elements, and in some instances in considerable quantity, assist in the formation of the animal structures. The most important of these are, amongst the non-metallic elements^ sulphur, phosphorus and chlorine; and amongst the metallic elements, potassium, sodium, calcium, magnesium and iron. By the combination of two or more of these different elements with each other, in varying proportions, several substances are formed, which, from the fact of their composing a great part of many of the animal tissues, have been called the proximate ele- ments of the body. These may be divided into those that contam nitrogen as an essential constituent, and those in which nitrogen is not present. Of the nitrogenous proximate elements, fibrine, albumen, caseine, gelatine and chondrine, are the most important. In addition to the nitrogen, these substances contain considerable quantities of carbon, oxygen and hydrogen, and a small propor- tion of sulphur and phosphorus. Fibrine exists b<\tk \&. ^kssw ))lood and muacleB. Albumen also cQQs\l&v3i^ «si ^s^^^^ss^^^^^j^s^-^ ffl INTKODCCTOHT. Btitnent, not merely of the blood and mnscleB, but also of most of the animal flaids, Caseine is fonnd in great abundance in the milk, and to a ulight extent alBO in the blood. Gelatine com- poses a conKidernble proportion of the bones, and it is also fonnd in certain of the softer tissnea, especially the fibrons. Chondrine eonstitntes the essential constituent of cartilage. Of the non- nitrogenous proximate elements, the various fatty matters, constituting the fat of the body, are the most remark- able. The most important of these ore composed of certain substances, to which the chemist has given the names of stearine, margarine and oleine. The more solid fats, such as suet, being composed to a great extent of stearine ; the more liquid or oily fats, consisting espentially of oleine. These different fatty substances all possess the property of forming a soap when digested with alkalies. There are certain other fatty prin- ciples, howeyer, which are not capable, of being converted into Boap. The most important of those is cholcstearino, a substance which is found in the bile and in the brain. Sulphur and phosphorus appear to be elements of groat import- ance in the building op of the animal textures. They are found together in the several nitrogenous proximate principles already described. Sulphur exists also in the hair, nails and cntfcle, and, to a small extent, also in some of the other testnres. Phos- phorus is fonnd, in considerable quantity, in the nervons tissues, especially in the brain. In combination with osygcn as phos- phoric acid, this substance assists in the construction of almost all the various tissues composing the animal fabric. This acid is combined with soda in the blood, with potash in the mnscleB, and with lime and magnesia in the bones and teeth. Chlorine also exists in appreciable quantity in the different tissues. It is generally combined with the metal sodium, forming the compound with which every one is so familiar, — chloride of Bodium, or common salt. There is probably no textnre in which a small proportion of this compound cannot be detected. The manner ia which thkeeXt is diffused thronghout the body explaint JHTBOPUOTOBY. 17 the desire for salt as «a article of food, and the great distress that Always supenneoes wh^ the system is deprired of it for any length of time. Iron also exists la small qns«i!tatiesia the great majority of the tissues, its aspedal seat, hoire?er, is the blood ; in the globules joi vMdi it forms an ^aential iuid eonsiderable eoostitoent. The Tsrioas elem^its abore deembed* and a fev others, which are mnch less generally diffused, and of Apparently minor Importanee^ are so combined in the animal ite^ ves, that they cannot, by the naked eye, or by any ordi&ary mode of obseryaticmy be discovered. The tissues composed of them tntist be subjected to the action of powerful chemical agents, when, by the a^licatiou of the appro- priate tests, they may each of them be detected. General Functions. — The functions performed by the tissues may be divided into two great classes : — Isty The functions of organic or vegetative life. 2d, The functions of imimal liDa. The first class has derived its name from this circumstance, that the functions composing it are performed by all those beings which possess that mysterious principle called life, whether they be plants or animals* These fcmjctions are not necessarily per- formed to the same extent, or in the s^'me manner, in all the various subdivisions of :(he orgam;sed world. They principally minister to the preservation jQf life^ and axe consequently employed in the Absorption of nutritive material or food from without ; in ihid circulation of this nutritive material throughout the sys- tem ; in the a^imilation of it to the different textures of the body, so as to assist in their growth and nudntenance ; and in its puri- fication, especially through the functions of respiration and aecre- JAoa. The fiinetions of .aaaimal life are performed exclusively by ammah. These ;axe e^)6cially manifested through the agency of tb« n^*vous system, auid the various sensory and motor organs •ioonoected wiih iU The most characteristic animal {a£.u\Vj \& ^qv^^v^'s^^cl^^^ ^^1 18 1 which the creature becomes cognisant of impreasionB made npon it from without, or of certain changes taking place in its own Btructnres, which it is enabled to comprehend throngh sensation. Another of these animal faeulties is that of voluntary motion, by which the animal can move either ita entire body, or parts of it, from one locality to another. Iq man the functions of animal life greatly preponderate, and exercise a great influence over those of organic life. This is owing to the circnmstance, that in him the nervous system is greatly developed, in accordance with the possession of his superior mental attainments. We will now proceed to consider more in detail the different tissues, and the fanctions performed by them. |L .z:. J ^^^^^^^^E THE SKELETON. ^^BP^H Is order that the form of the body may be properly preserved, its various parts kept in doe position, and the different functions required of it efBciently carried on, it is necessary that it should possess a solid frame-work or support. This is given to it by the presence in ita iutorior of a firm, hard material, called Bone. The difTerent bones found in the human body are composed of this material. The name of Skeleton is given to the bones when placed in such a position as they occupy in the living body. Fig, 1 is a front view of an adult skeleton. If the eye is cast over it, it will be seen that the bones may be naturally divided into those that occupy the head and neck, those that are found in the trnni, and those that lie in the extremities. Certain of these bones, which bear a great resemblance to each other in shape, and which evidently belong to the same group or series, bare been classed together under a common name. Thus all \ THE SKELETON. V 19 the bones fonning the spinal colomn are called Yertebrae. The great majority of thebonesjhoweyer, possess special and distingnish- ing names. To some names have been given, which express the locality or position which they occupy in the living body, as bone of the forehead, bone of the thigh, etc. To others names have been given which indicate peculiarities of shape, or some supposed likeness to geometrical figures, or well known objects ; — ^thus th^ are the cuboid bone, the ploughshare-shaped bone, the boat- ^ shaped bone. These names were applied many hundreds of years ago by the old writers on anatomy ; and although in some instances the bones do bear some general resemblance to the objects after which they are called, yet this is often far-fetched and fanciful. We will, in the first instance, name the bones, according to their division into the parts already indicated. Bones of the Head and Face : — 1. Bone of the Forehead (Frontal bone). 2. Bone of the Side of the Head (Parietal bone). 3. Bone of the Back of the Head (Occipital bone). 4. Bone of the Temple (Temporal bone). 5. Wedge Bone (Sphenoid). 6. Nose Bone (Nasal). 7. Bone lodging the tube down which the tears pass (Lachrymal bone), 8. Cheek Bone (Malar). 9. Ploughshare-shaped Bone (Vomer). 10. Upper Jaw Bone (Superior Maxilla). 11. Lower Jaw Bone (Inferior Maxilla). In addition to the above-named bones, there are others which enter into the formation of this division of the body. The Sieve bone, or Ethmoid, called from its presenting on one surface a nmnber of perforations like a sieve, is, for the most part, so con- cealed by the other bones, that it cannot be seen in the figure. A small portion, however, appears at the inner wall of the orbit. On the outer wall of each nostril is a bone, which, from being peculiarly turned on itself, is called Turbinated ; and at the back part of the roof of the mouth are a pair of bones called Palate, but these cannot be seen in the figxite, T!:\i<^\iOTft^ ^1 ^^V^'^ 50 THE SKELETON. iebcj^l and face are tlius very nnmermis ; many of thera are single b< but the majority are arranged as pairs, one on each side. They nnmber altogether tweaty-two bcpnes. The Dnmher and com- plexity of shape of these hones depend upon the subdiriBion of the skull into-certain distinct chambers or cavities, for the recep- tion or transmission of important strnetures. Several of the bones enter into the formation of more than one of these chambere. The most important and largest of the cavities is that which contains the brain. Its roof and side walls are formed by the bones marked 1, 2, 3, 4, which, together with the wedge and siere bones, constitnte the bones of the skall. Certain smaller cavities' opening upon the face are likewise formed partly of these bonea, and partly of the bones of the face. Thus — a Bepresents the Cftvity of the OrTiil, in whioh the Eye ii lodged. b The Cavity of the Nose, divided into two parts bj a partittoo com- poaed in part of the Vomer. c The Cavity oflie Month, closed in by the Teeth. Boues of the Spinal Colomn or TertebrjB : — The Rpinal column consists of twenty-six bones, placed one above the other. The two lowest of these bones are, in childhood, composed of Beveral Bmaller bones, which in the adult become Joined together, hence they are termed the false vertebrie (15, 16). The rest are called the true vertebrae. Their name is derived from the Latin verb, verto, to turn, because they turn slightly on each other in the various lateral movements of the trunk, The Trne Vertebrm are 24 in number : they are divide^ three portions: — IS. ■VeriebriB of the Neck — 7 in number. I. Vertabc4B of the Choit— la in nnmber. I. Tertebric of the Luins — 5 in number. (Seeulsoi'ig. a,) jThe False TertebrK, consisting m the adult of two bonefl med Vertebrte of the Pelvis. i. SacnuD. IG. Covi^yx. This is the bone whiub is uoDiider&bly elongated ia malf possessing a tail. THE SKELETON. 21 Fig; 2 is a side view of the spinal colmxm. The vertebrsB are represented as being separated from eadi other by a small interspace ; this is filled up in the Hying body with, an extremely elastic substance, the intervertebral' substance, re- presented in the ligamentous plate. The sides of the 10th, ilth^ and 12tfa yertebrae of the chest, and that of the 1st yertebra of the loins, have been removed in order to expose the canal lod^d in the interior of the spinal columv which contains the qnnal cord. Projecting from each of the different vertebrffi making up the column are several strong processes of bone; some of these, such as a and c, have muscles attached to them; others, as &, see for the purpose of assisting in mdtmg each bone to those situated immediately above and below it. €L. represent the outer surfaces of theshouldeif and hip joints. The ligament that especially characterizes this form of joint is the membranous or capsular. It completely surrounds the arti- cular surfaces of the bones, enclosing them, as it were, in a bag. It is connected by one extremity to the outer surface of the socket, whilst by the other it firmly embraces the constricted part, or neck of that bone on which the head is situated. This kind of ligament allows great extent of movement to take place in the joint, the ball or head of the long bone being permitted to roll about in every direction. The ball and socket joint may be very ftilly illustrated by examinm!^t\s& jou^^H 42 JOINTS AND UGAMENTS. Fig. 3 represents a yertical eeotion of the right 1 show its internal Btrnctnre. a. Articnlar Cartilage. b. Synovial Membrane. c Capsular Ligament. The synovial membrane may here be traced lining the inner Burfaco of the ligament, and covering the articular cartilage. In thisjoint the capsixlar ligament is not the only agent which retains the bones in their proper position, for the fibrons ring, berore described as deepening the socket, closely clasps the articnlar end of the thigh bone, and thus materially assists in retaining the articnlar surfaces closely together. The action of this fibrouK ring has been compared by some anatomists to that of the com- mon leather sncker employed by boys for raising stones or other weights from the ground. It so closely embraces the thigh bone that neither air nor fluid are permitted to he between the arti- cular surfaces. Hence the pressure of the atmosphere acting upon the exterior of the thigh, forces the ball into the socket, and keeps it there. In the interior of the joint is a strong band of fibres called the interarticular or suspensory ligament (d.) This is connected by its upper end to a depression a Uttle above the centre of the head of the thigh bone, by its lower end to the lower margin of the great hollow (acetabulum) in the haunch bone, which receives that head. When a person is standing erect, or with the body slightly bent, a portion of the weight of the trunk is borne directly by the heads of both thigh bones, or of one thigh bone, according as he stands upon one or both legs, owing to the direct pressure of the acetabula npon the heads of those bones. Now, as the end of this hgament that is connected to the lower margm of the ace- tabulum is much lower than the end cotmected to the tliigli bone, it of necessity suspends that portion of the weight of the b witiA /a tbronrn Upon it. debi^^ JOINTS AND LIGAMENTS. 43 The effect of this is, to distribute otrer the head of the thigh bone that weight which, supposing the suspensory ligament had not been present, would have been sustained by that portion merely which is in direct contact with the upper part of the ace- tabulum. The hip and shoulder joints possess very extensive movements. Of the two the hip is the least moveable, because upon these joints the whole weight of the body is thrown in the act of stand- ing, so that, having to bear at times considerable pressure, they are required to be of a deeper and firmer construction than the sboulder. Hence, in them we find the bones much larger, the sockets for the reception of the heads much deeper, and the con- necting ligaments much more tense and strong. The shoulder, on the other hand, in order that free play may be given to the arms, has a shallow socket, and a capsular ligament, which is much more lax than the corresponding structure in the hip. The Hinge Joint has its best representative in the elbow. The knee-joint and the joints of the fingers and toes also present examples of it. The kind of ligament that more especially characterizes this form of joint is the lateral ligament ; so that in aU hinge joints strong ligaments may be found on each side. These vary slightly in their shape, some being flat, others rounded ; but they all agree in this respect, that they possess great strength. They are connected by their extremities to projections at the sides of the ends of the bones* which they bind together. It is essential to the proper working of the hinge, that the surfaces should move backwards and forwards upon each other, without any lateral displacement taking place. This is attained by the mode of connection of the strong lateral ligaments. The knee-joint, firom its great size, possesses very well marked lateral liga- ments. Pig. 1 (m.) gives the external appearance of the elbow-joint. Fig. 4 exhibits the appearance of the interior when the IL^ar meot IB iivntk cut across. 3 44 JOINTS ASD LIGAMENTS. a. Articular Cartilage, b. Synovial Membrane. Although the ends of threo bonee, A. Humenw, u. Xnna, r. SatiiuB, are Been, yet it is only between two of them, the humerus and uhia, that the proper moveraenta of the hinge are performed ; these raorementa are forwards, termed flexion, and backwarde, termed estenaion. The accuracy of these movements is in- sured by tlie presence of a pulley-like surface on the humerns at a, to which a ridge on the articular surface of the ulna closely corresponds, fitting into it, and moving readily in it in the backward and forward action of the joint. The radius, from its close connection to the ulna, mores back- wards and forwards along with it, yet it cannot bo said to form an essential part of the hinge. It posaosses, however, a very beau- tiful movement of its own upon the ulna, for ita head is closely confined within a ring, represented in Fig. 5 (a.), formed partly of a smooth concave surface on the outer side of the ulna, and partly of a strong annular ligament connected to the ends of this surface : within this ring the head of the radius rolls. The movement between these bones is effected when the hand, placed on a flat snrface, with the palm downwards, is turned bo that the palm looks upwards ; this is called supination of the hand and fore-arra. When the hand is again returned to its original position, the movement of pronation ia performed. The joint be- tween the upper ends of the radius and nlna la not, however, the only one concerned in the production of these movements. For a corresponding joint esista also at their lower extremities ; only at this latter joint tie radios has the concave surface, to which a convexity at the end of the ulna corresponds. The radius is the moveable bone, the uba remaining in its position. So that, owing to the exactly opposite arrangement of the articular ex- treaiticB of the two bones, daring ^Tonatioo. and supinatioii, JOINTS AND UGAMENXS. 45 whilst the upper end of the radios rolls in the cftTity of the nlna, its lower end may be regarded as reyolving aronnd the convexity of the nlna. The steadiness and delicacy of these movements are also increased, when the elbow is bent, by the cap*shaped cavity at the head of the radius receiving the small rounded surface of tiie part of the humerus corresponding to it. A sort of central point or axis is thus afforded, upon which the movements take place. Hence, when it is necessary to perform any movement with the fore arm, in which pronation and supination are to be called into action, and which requires either strength or preci- sion for its execution, the elbow is always bent, for the radius now possesses a fixed point upon which it can move. This may be illustrated by the common operation of inserting a corkscrew into a cork. This is effected by the altemation of these two movements, and, as may readily be ascertained by trying it, is much more easily done when the arm is slightly bent, than when it is extended. There is no movement, between the two bones of the leg, cor- leq^onding to that of pronation or supination performed by the two bones of the fore arm ; for the leg, being for the purpose of supporting the weight of the body, it is necessary that it should be strong and steady. Hence the joints between the upper and lower ends of the tibia and fibula are of such a nature as to allow scarcely any movement at all to take place between the two bones. Owing to the ligaments connecting the different bones in a finger beiug lateral ligaments, the movements possessed by these bones are flexion and extension. These kinds of movements, together with the numerous joints, eminently adapt the hand for the performance of its various duties. Thus, the diffident joints in the fingers can be so b^t that each finger may be made to assume the form of a hook ; the bending of the whole of the fingers, in this hook-like maimer, enables us to su^nd the whole weight of the body upon an object grasped by 4hem. Th^ movemantihat especially characteriBe&t\ki^\i«6DLdLcA^GQ^^ 46 JOIXTB ASD LTGAMEKTS. ^M of oppoBition ; that is, by which the thumb can be made to «^ pose or touch uny part of the pahnaj- surface of the hand and fingers. This gives to the haad nnusnal power in grasping objects, and compressing them, if needful, with great force, whilst this force can be bo nicely regulated, that movements requiring the most delicate manipulation can be undertaken with equal rcadiuesE. movements of Joints — The different movements capable of beuig performed by the jomts, may be classed together nnder the names of gliding movement, opposition, and rotation. The ghding movement is the most simple — it is merely the moving of two nearly flat surfaces upon each other. It is ob- served in the joints between the different vertebrae, and in the articulation between the occipital bone and first vertebra. Nodding of the head, either forwards or backwards, is per- formed when the last two bones glide upon each other. In Fig. 7 (n), the smooth surface of the first vertebra, on which the oc- cipital bone glides, is seen. Opposition, or the angular movement, is the movement of a joint in opposite directions, as in bending a. limb, flexion, and extensioQ, making it straight again. Numbers of the joints are capable of performing these simple movements. Or the move- ment of a limb outwards, termed'ab duct ion, and inwards, adduc- tion, the latter taking place when both tliighs arc brought to- gether. Wlieu a single joint can be both flexed and extended, ab- dncted and addncted, it is then said to be capable of performing the movement of circumduction. The hip and shoulder joints funush examples of this. This movement is very extensive in both these joints, for, by swinging either the arm or leg round, the tips of the fingers or toes con be made to describe a consider- able circle. Rotation, where a bone tnruB upon its own axis, is possessed, to a ceitaio extent, by both the hip and shoulder joints, foi,iE^ /ie ami bone or tbigh bone be grasped, they may be madft. i JOINTS AND LIGAMENTS. 47 rotate partially upon their own axes. It is seen, however, in the greatest perfection in the joint between the first and second ver- tebrse of the neck. In Fig. 6 and 7, the parts between which the rotation is performed are represented. Fig. 7 is a view of the first and second vertebras, seen from above, the occipital bone having been removed. 1 First Vertebra (Atlas). 2 Second Vertebra (Axis). Springing from the npper surface of the body of the axis is a strong process of bone (b). This process fits into a sort of ring, formed by a hollow on the inner surface of the atlas (c), and a strong ligament stretch- ing across between the sides of that bone, the transverse liga- ment (d). This process is still further kept in its place by strong bands which extend from the transverse ligament, upwards to the occipital bone, and downwards to the axis. In Fig. 6 the outer surface of these ligaments is seen from behind, the back of the occipital bone and the hinder part of the atlas having been removed in order to afford a view of the interior of the spinal canal, in which the process of bone and its confining ligaments are situated. 1. The Atlas. 2. The Axis. 3. Occipital Bone. a. The Transverse Ligament. b. The Ligament going from it to the Occipital Bone. e. The Ligament passing down to Axis. By means of these ligaments the strong process of the second vertebra is retained in its position. When the head is moved from side to side, ue.^ when it is rotated, the atlas, to which it is firmly connected by ligaments, revolves around this bony process, which thus acts as a pivot or axis, hence the xiame of axis applied to the second vertebra, from which it springs. The rolUng movement is facilitated by the presence of two synovial membranes, (e.e.) Fig. 7, oik<& ot ^\i<(^\^ ^\^^e)X^ 48 JOISTS AITO LTGAMENTS. between the front of the process and tho atlas, the other lying between the back of the process and the transverse ligament. It will thus be observed that the nodding and rotatory move- ments of the head, take place at different joints, the first being between the occipital boue oud the atlas ; the second between the atlas and the axis. In addition to the ordinary apparatns of h'gamentg and synovial membranes connecting the different vertebne, there is placed between ea«h of these bones a structure of a peculiar nature, which has been termed the intervertebral substance or cartilage. This consists of a series of disc-like bodies, corresponding in shape to the vertebrse between which they are placed, and to which they are firmly united by their two surfaces. Fig. 8 represents the upper surface of one of these discs. It is seen to be composed at its circumference of a number of layers, arranged in a concentric manner, and closely united to- gether, the interior of the disc consisting of a soft spongy sub- stance, which does not exhibit any regular arrangement. Fig. 9 is a view of three of the vertebras with the dkcs be- tween them. The discs vary in thickness in different parts of the spinal colnmn. In the regions of the neck and loins they are thicker in front than behind, exactly the opposite being observed m the discs placed between the vertebra of the chest. It'is owing to this circumstance that the spinal column ia not straight, but curved, being convex forwards iu the two first-named regions, whiist it is concave forwards in the region of the chest. The anterior concavity of the spine in this region necessarily increases the size of the thoracic cavity, and affords a greater amount of space for the expansion of the Inngs to take place in, during in- spiration. The intervertebral substance is highly elastic, a property which is of the most essential service ; for the vertebrd colanm con- taias ia its hiteriot the spinal canal, lodging the spinal cord, and THE MUSCLES. 49 it has connected to its upper extremity the cranium, which con- tains the brain. Both the brain and spinal marrow are very deticate organs, and extremely susceptible of injury. To the spinal column is transmitted the whole weight of the body in its various movements of walking, running, leaping, etc. The elas- ticity communicated to it by the presence of these discs, preserves both the column itself, the spinal cord contained in its interior, and the brain placed at its upper extremity, from the injurious effects that would otherwise be produced by these movements. In addition to the elasticity produced by the presence of the discs, the number of joints between the different bones of the column, the bony surfaces of each joint possessing their own plates of elastic cartilage, and the peculiar elastic ligaments be- tween the different arches of the vertebrae, add considerably to this property. A very curious circumstance has been observed with regard to the height of the body at different periods of the day. If a person has been standing during a great part of the day, or actively moving about, he is found to be about an inch shorter than he was when he arose in the morning. This is owing to the weight of the trunk pressing continuously for a length of time upon these elastic discs, so as to force the surfaces of the bodies of the ver- tebrsB more closely together. Rest, however, in the horizontal posture, as in bed, by removing the cause of compression, enables the discs to recover their proper size. CHAPTEE IV. THE MUSCLES. The muscles are the organs of motion — ^that is they are the agents by means of which the movements, either of the whole body, oT its mdiridnal parts, are effected.. 50 THE MUSCLES. The mnscles are divided into two great classes. Those composing the first class are the true organs of locomo- tion, the agents by which the body is moved about from place to place. These are called Voluntary muscles, for they are under the power of the will. Those making up the second class are placed within the cavities of the body. They possess no power of changing the position of the body, for they act merely upon the organs to which they are connected. They are called the Involuntary muscles, for the will has no power over them. It must be understood, that in this chapter the voluntary muscles are alone referred to. Fig. 1 represents the muscles placed on the front of the body. Only the most superficial muscles are represented. That is those placed immediately beneath the skin and muscular fascia. Their natural position is observed. It must be understood, however, that beneath these muscles many others are situated, which can- not be represented in. the figure. Muscles of the Face, Head, and Neck : — 1 . Muscle of the Forehead. This, together with a muscle at the back of the head, has the power of moying the scalp. 2. Muscle that closes the Eyelids. The muscle that raises the upper eyelid so as to open the eye, is situated within the orbit, and con- seqaently cannot be seen in this figure. It is represented in Plate 8, Pig. 2, S, the Senses. 3, 4, 5. Muscles that raise the Upper Lip and angle of the Mouth. 6, 7. Muscles that depress the Lower Lip and angle of the Motith. By the action of the muscles which raise the upper lip, and those that ^' depress the lower lip, the mouth is opened. 8. Muscle that draws the Lips together, so as to close the Mouth. 9. Muscle of the Temple. , 10. Masseter Muscle. 9 and 10 are the two chief muscles of mastication, for when they contract, the moveable lower jaw is elevated, so as to crush the food between the teeth in the upper and lower jaws. 11. Muscle that compresses the NostriL Close to its outer side is a small muscle that dilates the nostril. /^. Muscle that wrinkles the skin of the "Neck, THE MUSCLES. 51 13. Muscle that aflsists in steadying the Head» and also in moring it from side to side. 14. Muscles that depress the Windpipe and Organ of Voice. The mnscles that elevate the same parts are placed beneath the lower jaw, and cannot be seen in the figure. Muscles that connect the upper extremity to the trunk. For lions of four of these muscles axe represented in the figure, viz : 15. Muscle that elevates the Shoulder. — Trapezius Muscle. 17. Great Muscle of the Chest, which draws the Arm in front of the Chest (Great Pectoral Muscle"). 18. Broad Muscle of the Back, which draws the Arm downwards across the back of the Body (Latissimus Dorsi). 19. Serrated or saw-like Muscle, extends between the Kibs and Shoul- der-blade, and draws the Shoulder forwards. At the lower part of the trunk, on each side, may be seen the large muscle which, from the direction of its fibres, is called, 20. Outer oblique Muscle of the Abdomen. Several muscles lie beneath it. The outlines of one of these, 21. Straight Muscle of the Abdomen, may be seen beneath the ex panded tendon of insertion of the oblique muscle. These abdo- minal muscles by their contraction possess the power of compress ing the contents of the abdomen. Muscles of the upper extremity : — 16. Muscle that elevates the Arm (Deltoid Muscle). 22. Biceps, or Two-headed Muscle. Represented in Fig. 4. 23. Anterior Muscle of the Arm. This and the Biceps are for the pur- pose of bending the Fore-arm. 24. Triceps, or Three-headed Muscle. Represented in Fig. 5. This counteracts the last two muscles, for it extends the Fore-arm. 25. Mass of Muscles that bend the Wrist and Fingers, and pronate the Fore-arm and Hand — that is, turn the Hand with the palm downwards. They are called the Flexor and Pronator Muscles. 26. Mass of Muscles that extend the Wrist and Fingers, and supinate ,. the Fore-arm and Hand — that is, turn the Hand with its palm upwards. They are called the Extensor and Supinator Muscles. 37. Muscles that constitute the ball of the Thumb. They move it in different directions. • S8l Muscles that move the Little Finger. 52 THE MUSCLES. Muscles that connect the lower extremity to the trunk. Several are represented in the figure. 29. Muscle usually stated as having the power of crossing one Leg over the other, hence called the Tailor's Muscle, or Sartorius ; its real action is to assist in bending the knee. 30. Muscles that draw the Thighs together (Adductor Muscles). 31. Muscles that extend or straighten the Leg (Extensor Muscles). One of these, viz., the straight muscle of the thigh, is represented in Fig. 2. The muscles that bend the leg are placed on the back of the thigh, so that they cannot be seen in the figure. Muscles of the leg and foot : 32. Mass of Muscles that bend the Foot upon the Leg, and extend the Toes. 33. Muscles that raise the Heel— these form the prominence of the calf of the Leg. They are more fully represented in Fig. 6. 34. Muscles that turn the Foot outwards. The muscles which turn the foot inwards, so as to counteract the last named muscles, lie beneath the great muscles of the calf, which consequently conceal them. The foot possesses nu- merous muscles, which act upon the toes, so as to move them about in various directions. These are principally placed on the sole of the foot, so that they cannot be seen in the figure. Only one muscle, which assists in extending the toes, is placed on the back of the foot This is represented in the figure. The above, although consisting of but a small number of the muscles of the body, yet serve to illustrate their nature and uses. The names given to the muscles generally express either their position or size, their shape or uses. For example, the great pectoral muscle, 17. This receives its name of pectoral from its position. It is also called great, in order to distinguish it firom the small pectoral muscle which lies beneath it. Several muscles have the names of biceps or triceps given* to tbeiDf because they possess two or tiwcee diatmftt, \i^d& of ori^, THE MUSCLES. 53 as in the biceps, 22, and triceps, 23, in the upper extremity. The name of extensor, or flexor, or elevator, expresses that that office is performed by the muscle so called. The exact number of muscles in the human body varies ac- cording to the methods employed in enumerating them ; about 400 may be considered as the received opinion. The muscles are placed beneath the skin and the fat that is found under it ; they are also surrounded, especially in the neck and extremities, by a strong membrane, called a fascia^ which may be compared to a thin flattened ligament, for it is composed of the same tissue — ^the fibrous. It not only surrounds the whole mass of muscles, but it also sends thin partitions between the different muscles, so that each is separated from its neigh- bour by a fine piece of this membrane. In Plate YII., the Ner- vous System, this fascia is represented on one of the legs. The use of this fascia is to retain the muscles in their proper positions during their action. For when a muscle contracts, a certain amount of movement necessarily takes place in it, so that, during violent action, it would have a tendency to slip or move out of its position. This is counteracted by this fascia, which binds the muscles together. Hence it is par- ticularly well marked in all those parts, such as the extremi- ties, where the muscular action is frequently strong and long continued. The musdes are of a bright red colour, and constitute what is called the flesh. They make up the great mass of the body, the weight and bulk of the individual for the most part depend- ing upon the volume of the muscles, whilst the height is owing to the length of the bones. The muscles in those parts of the body that are most frequently used, are larger and stronger than those found in parts less frequently employed ; thus, the • muscles on the right side, especially those of the right arm, are bigger and more powerful than the muscles on the left. Divisions of Muscles. — ^From the figure it will b^ ^^\s.tVial^^ifc muscles present considerable differences m ^a^^^ ^V^-^ tbsj^ 54 THE MUSCLES. ^H be (liyided, liowerer, into the two great classes of broad asft long muaclea. The broad muscles are met with in tlie trunk ; some of the maacles of the face also belong to this division. The great mnacle of the chest (17) and the obliqne muscle of the abdomen (20) are good examples of broad muscles. The Bhape of theee muscles especially adapts them for the positions that they occnpy, for as they have most commonly to aasiat in forming the wall or boundaiy of a cavity, their ex- panded shape enables them to do this readily. The long muscles are seen to the best advantage in the ex- tremities ; examples are also furnished by some of the muscles of the face and neck. Naked Eye Stiuctore of Muaoles. — A muscle may generally be dirided iuto three portions — a central part or belly and two estremities. The centre is commonly the largest of tlie three divisions, from which it in many instances gradnaliy diminishes in size towards either end. Pig. 2 illnstrates these divisions. The mn sole represented is the straight muscle of the thigh, which forms a part of the great extensor muscie of the leg. I. Central Bellr. t Upper Extrcmitf . ir Extremity. •■ The belly is composed almost entirely of muscular fibres — ^the structure of which will shortly be explained — but the extremities consist of an entirely different tissue, called tendinous, which closely resembles in its structure that of ligaments already de- scribed. The tendons formed by this tendinous tissue are popularly called the sinews. From the tendon at one extremity , the muscular fibres spriug, from it they extend to be comaected to the tendon at the other extremity ; they come to an abrupt termination as soon as tiiey reach the tendon, for the two tissues, tendinous and muecnlar, do not combine, beiug perfectly distinct m tbeir Etractare. The manner in whiiiK these two tissues be- THE MUSCLES. 55 come anited varies in different muscles. In Fig. 2 the mnscnlar fibres terminate on both sides of the tendon, like the barbs upon the shaft of a feather ; they are then called doubly penniform. In other instances, l^ey terminate upon one side merely, and then they are termed singly penniform. The tendons are con- nected to the bones, and thus they are the bond of communica^ tion between the muscular fibres and the bones. Mode of Ooimection of Muscles. — The two extremities of a muscle are connected to different bones ; in no instance are they • attached to the same bone. In Fig. 2 the upper e^ctremity is connected to the haunch bone (d), the lower to the knee pan (e), and, by means of the broad ligament extending from it, to the inner bone of the leg (/). These points are called the or^n and inaerdon of the muscle. When a muscle moves, it is said to contract, that is, its ex- tremities approach closer together, the belly at the same time swelling up ; by this contraction the two ends are approximated. This causes the two bones to which the ends are attached like- wise to be drawn nearer to each other. In order that this may be efficiently performed, one end must be comparatively fixed, so that a steady firm point may be afforded upon which the muscle may draw; the fixed point is the origin of the muscle; the moveable, or that which is drawn towards the fixed, the insertion, jb the straight muscle of the thigh, the end connected to the haunch bone being the fixed point, is the origin of that muscle, the end connected by means of the knee pan with the inner bone of the leg, the insertion. The muscles of the face have only one extremity (the origin) connected to bone, the other (the insertion) being attached to 9kin of the face: owing to this pecoliarity, when the facial muscles contract, they move the skin, and thus produce all those various expressions, by means of which the passions and emotions are depicted upon the human countenance. There are certam of the muscles of the face that have no cou- nectioo to bone at all i these fire {he iD?9Ad<^ ^i!cv^ ^.^kv^^"^^ 55 THE MUSCLES. , SK openings of the eyes and month. Their shape is peculiar, they are composed of a number of fibres arranged in the form of an oval or ellipse, the fibres surrounding the opening, towards which their concave margin looks. When they contract, the space between the fibres on the opposite sides of the ellipse is gradually diminished, until the orifice is completely closed. They are represented in Fig. 1 (2, 8) as in the contracted state, the mouth and eyes being shut. They are called orbicular muscles. Kuscnlar Action. — The extent of movement of a muscle Ib proportioned to the length and direction of the muscular fibres composing it. In the limbs, where great extent of movement is required, the muscles, as a rnle, possess considerable length of muscular fibre. Amongst the most remarkable of these ia the sartoriuB, 29, which possesses longer muscular fibres than any other mnscle in the body. Certain of the muscles of the estremities also possess very long tendons — a circumstance which enables them to be attached at some distance from the part that they move i if this were not the case, the limbs, instead of gradually tapering towards a joint, would be thick| heavy, and cumbrous at that part, owing to the necessary crowding together of a large mass of muscular fibres. The great length of tendon thus removes the two extremities of these muscles away from each other, so that they frequently pass over two or more joints, upon all of which they possess some influence, for when, daring contraction, their action has been expended upon one joint, a continuance of the contraction enables them to act upon another. The two muscles that bend the fingers furnish examples of this kmd. These muscles are strong and fleshy in the fore-arm ; but as tliey pass over the wrist-jomt they become tendinous, the muscular fibres no longer existing in them. From each muscle a tendon passes to each of the fingers, one to be connected to the middle phalanx, the other to the last phalanx. As the ten- flfan* pass aJong the front of tlie fingeta, tte'j ate confined in THE MUSCLES. 57 strong sheaths by bands which are attached to bo A sides of each finger (Fig. 1 a,) A synovial fluid lubricates the interior of the sheath and the surface of the tendon, so that it moves with great ease and smoothness in the sheath which contains it. These tendons pass over the wrist-joint as well as the joints of the fingers. When they first begin to contract they bend the fingers ; if this contraction continues they bend the wrist, so that by their action the entire hand is flexed upon the fore-arm. As the extent of movement of a muscle is regulated by the length of the fibres, so the power of contraction is proportioned to the number of fibres contained in it. Short muscles, con- taining a considerable number of fibres, may thus possess great strength of action. Amongst these may be mentioned the tem- poral and masseter muscles, which are such important agents in the process of mastication. When a muscle contracts, it does so by the influence of the Will. When we desire to perform an action, such as raising the arm, we will that the muscles by which this is performed should contract, and the arm is elevated. This action in most instances is so rapid, that there is scarcely an appreciable inter- val of time between the willing and doing of the action. The Will possesses the power of decreasing and of increasing the force of muscular contraction up to a certain extent ; and it can estimate, in the great majority of instances, the amount of force that has to be exercised in the performance of a given move- ment. The will is the natural stimulus for exciting muscular action, the stimulus being conducted by the nerves which proceed from the brain or spinal cord to be distributed in the muscle, in which, in a manner that cannot be explained, it induces contraction. All the voluntary muscles are thus brought under the influence of the will, some apparently to a greater extent than others. For there are certain muscles, whose structure exactly corresponds to that of the voluntary muscles, yet which are only ijattlftXl^ controlled bjr the wUL The most imporlMsV. qI ^^'sfc «s^^ '^^ 58 THE anjSCLES. mnsdea subservient to reapiration, tiie action of whicli tlie will can only control for a short period. The nervous force induced by the will is the only agent in the living body which naturally excites the action of the voluntary muscles. Certain other stirauii may be made to induce artificially their contraction. The most remarkable of these is electricity, a current of which, if sent either throagb a muscle, or through the nerve going to it, induces coiitraction. Any one of the numerous movements of the body, how- ever simple it may appear to be, is but rarely executed by a single muscle, for the muscles are generally grouped together, and associated for the production of regular move- ments. The muscles are bo arranged on the various parts of the body that they antagonise each other in their actions, — for example, the muscles of the extremities on one surface possess difiereut actions to those on the other ; thus in the arm the groups of muscles in front bend it, those on the back make it straight again. When one set contracts, it has not only to move the arm, and anything that may be connected to it, but it has ateo to overcome a certain amount of resistance offered by the mnsules of the other set, which are called the opposing muscles. When the muscles oa both enrfaces contract at the same tune, and with the same amount of force, then the part no longer moves. The some arrangement of the muscles into groups, with oppos- ing actions, is seen in the lower as well as the upper estremity. By the alternate action of tliese groups t!ie limb is bent aud made straight again, as in tlie act of walking. During exercise, espe- cially if it is violent, the contractions and relaxations of the maecles alternate with each other with great rapidity. As these are taking place, certain changes occur in the substance of the mnscle, by which its particles are, as it were, wasted or worn away. When this has gone on for some lime, the muscle Hres, and that feeling of fatigue is produced, which, as is well kuown, alM-ujs accompanies considerable exertion. IE the muscle is now THE MUSCLES. 59 aUowed to rest, it gradually recovers itself, and is again enabled to perform its usual functions. HioxoBCopiA Stmoture of Muscles. — The structure of a muscle is peculiar* Each muBde may be readOy split up into a number of bundles, depending upon its size. Each bundle is separated from its neighbour by an exceedingly thm and deUcate partition, proceed- ing from the inner surface of the fascia, akeady described as investing the circumference of the muscle. Each of these bundles can be agam subdivided into a number of distinct fibres. These are represented in Fig. 3. If any one of these fibres (a) is examined under a powerful microscope, it will be seen to be composed of a number of most minute threads called fibrillse. The cut ends of these are ^n in the figure. These fibrillaB are dosely packed together, and surrounded by a transparent membrane (6), which retains them In position. The membrane has been removed from the outer surface of a few of the fibres (c), and the fibrillse separated from each other. The fibres exhibit, when highly magnified, trans- verse lines upon their exterior. This circumstance has given to the voluntary muscles the name of transversely striped. Between the fibres the small blood-vessels (d) that carry blood to the muscle are seen. The structure above described alone possesses the power of contracticm, for the tendon has no contractile power ; hence it must be considered merely as the inelastic strong band 0f connection between the contracting tissue and the part upon which it acts. Leverage of Musdes. — The attachment of the muscles to the bones, and the manner in which they move them, furnish ex- funples of the different classes of levers. The third kind of lever, wh^re the power is placed between the fulctum and the weight, is the one most commonly met with. Numerous examples of it are furnished in the musdes that bend the extremities. F'jg. 4 is a new of the biceps muscle ot \)ftft ^x^ *i^;»^^^^^% CO THE MUSCLES. this form of lever. Ilcre P rcprcseuts the place of attachment of the muBcIe to the radins ; it is the point at which the^power or raotive force is applied. P, the fnlcrum, ifi at the elbow joint ; and R, the weight, or resistance, at the hand. When the muBcle contracts, the forc-ann is bent upon the upper arm, the hand describing a curve as in the dotted line, This liind of lever appears to act in a disadvant-ngeous manner, for the power is attached to the hone close to the fulcrnm or centre of motion, and thus a greater amonnt of force has to be expended in pro- ducing a given result, than would have been the ease Bupposing the power had been attached nearer the weight ; but what is lost in power is gained in velocity, for R has to move throogh a large space in the same time that P moves through a much smaller one, and thus greater velocity is necessarily communicated to it, the rapidity of movement being equivalent in its usefolnesa to the losB of power. This property of rapid motion is more adapted to the retjuirements of the animal body than mere forc« of movement ; for a succession of less powerful, but quickly suc- ceeding blows, produces the same, if not a greater effect, than fewer, though more forcible ones. The power of the mnscle is, hovfcver, increased as its actios is continued, for at the first the tendon is inserted at aa acute angle into the bone, but aa the action goes on it is placed at a right angle to it, which is the most favourable for its action. Examples of levers of the second class, where the power is at one end, the fulcrum at the other, and the weight intermediate, are rare in the human body. The best instance is furnished by the muscles that depress the lower jaw, which are inserted into the inner surface of the chin on each side of the middle line, — these constitnte the power ; the fulcrnm is the joint of the lower jaw, the resistance to be overcome being the antagonistic power of the mnscles of mastication, Fig. 1 (9, 10), which are interme- diate to the power and fulcrum. There are several instances of levers of the first kind, where f&e power is at one end, the weight at t\>eot\i«t,»,ftd the fulcrum GENEBAL MECHANISM OF THE FRAME. 61 ■ intennediate. These are more especially seen in the extensor mnscles of the upper extremity. Fig. 5 is an illustration. The power P is famished by the attachment of the great extensor muscle of the fore-arm into the olecranon process of the ulna ; F, the fulcrum, is at the elbow joint, and R, the weight or resistance offered by the hand. Fig. 6 has been generally looked upon as an illustration of a lever of the second class. It represents the large muscles of the calf, which, from their attachment to the bone of the heel, raise it, together with the body, from the ground in the act of walk- ing,^ etc. It must be regarded, however, as a lever of the first kind, in which the power P, as in Fig. 5, is placed in a disadvan- tageous position, being connected to the bone close to the centre of motion F ; the resistance R, is at the earth, where the toes touch it, but as the ground, unlike the hand in Fig. 5, cannot be moved by the muscular contraction, the body is reacted upon, and it, together with the fulcrum, is raised. This happens when- ever we stand on tiptoe. If the foot is raised from the ground, and the same muscles put in action, the foot moves and not the body, for the ground no longer supporting it, the muscles act with sufficient power to overcome any resistance offered by the foot. CHAPTER V. GENERAL MECHANISM OF THE FRAME. The various structures that have been described in the preceding chapters, viz., the bones which constitute the supporting parts — the ligaments which bind them together — ^the joints, the sur- faces at which the movements take place — and the muscles, the agents by which these movements are effected — ^may be clsj&^^d together m the organs of locomotion^ A. ^^t^ ^^^x^ "c&n:^ \^^^ 62 GENERAL MECHANISM OF THE FRAME. be usefully devoted to the consideration of some of the prfnc^les which regulate the position, attitudes, and general movements of the whole framework. An inspection, either of the naked skeleton, or of the bones when clothed with their muscular covering, convinces us that the erect position is the proper attitude of man. The leading facts that prove this view are as follows : — The position of the head at the top of the spinal column. This is due to the articulation between the first vertebra and the base of the skull being placed almost in the centre of the latter, and not towards the hinder extremity, as in animals. The position of the face at the front of the head, and below the brain, the lower part not projecting before the upper, so that all its parts are almost on the same plane. Hence it is a matter of great difficulty to pick up anything with the mouth from a flat surface, as the ground ; so that there arises a necessity for hands and arms, by means of which food may be carried up to the mouth. The spinal column does not present in man that concavity along the whole length of its anterior surface, such as is seen in other animals ; although there is a curve with the concavity an- terior in the thoracic part of the spine, which would have a ten- dency to throw the body forwards ; this is counterbalanced by a curve in the opposite direction in the vertebrae of the loins and the neck, so that a perpendicular line may be drawn from the first cervical to the last lumbar vertebrae. The last of the lumbar vertebrae is connected to the broad upper extremity of the sacrum, which affords a wide basis of support ; this bone is attached, at its sides, to the widely ex- panded haunch bones, and, through the articulation of these, to the thigh bones, the whole weight of the trunk is thrown upon the legs, the bones of which, for this purpose,' are of considerable length and strength. From the width of the haunch the thigh bones are placed con- sidembly apart at the upper end, but mcKsaft tavTWc^ ^wib. other GENERAL MECHANISM OF THE FRAME. 63 at the knee, the upper ends of the tibia being broad and strong, in order properly to receive and support them. The foot is large and broad, placed at right angles to the leg ; the surface, called the sole, resting upon the ground, which it touches behind at the heel, and in front at the toes. It is arched in the middle, the hollow of the arch being turned to the ground, upon this arch the weight of the body necessarily falls. The movements of the legs, although sufficiently free for the performance of their proper office, viz., that of propulsion, are yet far less extensive than, those of the arms, as they have not merely to move the body, but also to support its whole weight. The arms, from their structure and extent of movement, are evidently not intended to aflFord support to the body. The free and varied actions of the shoulder joint ; the less extended yet more delicate movements at the elbow joint, especially those performed between the two bones of the fore-arm, termed pro- nation and supination ; the numerous minute yet decided move- ments of the hand and fingers, more particularly those by which the thumb can be opposed to the rest of the fingers, by which the power of firmly grasping an object, prehension, is attained, all point to some other purpose than that of mere support and pro- pulsion. The mass of muscles found on each side of the elbow joint are beautifully adapted to the movements of the articulation, and the general purposes of the upper extremity. If the arm bones are examined when the ligaments alone remain connected to them, it will be seen that when the elbow is bent, the fore-arm is drawn upwards and inwards, the palm of the hand touching the front sur- face of the body and the face ; this is evidently designed to aflFord protection to those parts in case of attack, and also to convey food to the mouth ; the contrary movement of extension draws the fore-arm backwards and outwards ; the muscles by which these movements are eflFected being placed at those points where they can best perform them, the flexors which beivd^^^L^^^^^^- mAoTs wMcb draw the arm inwards, aTlBmgfeom\Xi<&\KCkax\iQt^9 r h. Right Ventricle. c. Left Ventricle. d. Right Auricle. e. Left Auricle. The muscular partition, p, separating the two ventricles from each other, as well as the partition, p, separating the two auricles, is also seen. The opening of these three vessels into the right auricle may be observed. g. Upper Vena Cava. h. Lower Vena Cava. f. Coronary Vein. The coronary vein returns to the auricle the blood that has been carried to the wall of the heart by the coronary arteries. Its orifice is guarded by a small valve. The orifice of the lower vena cava is also guarded by a valve («), but the upper vena cava has no valve protecting it. This cavity conmiunicates with the right ventricle through u^ indicated by the arrow. At this opening is the large valve (v). The right ventricle again opens at i into the pulmonary artery, the valve (w) being at the orifice. Opening into the back of the left auricle are the four large pulmonary veins (x) proceeding from the lungs. There are two on each side. They do not possess valves. This cavity com- municates with the left ventricle, a valve (y) being situated at the place of junction. This ventricle opens into the aorta (Z), and here also a valve (z) is placed. The cavities above described are bounded by the contractile muscular walls of the heai^t. The valves situated at the various orifices are all represented as being open. In Fig. 4 the arteries and auricles have been removed ; the ventricles, with the valves separating them on the one hand from the auricles, and on the other from the arteries, being shown. The valves are all represented as closed, their \i^^^^ ^^al'Msfc^ hemg seen. 70 THE HEABT AND ABTEBIES. b. Right Ventricle. c. Left Ventricle. I. Pulmonary Artery. L Aorta. The valves that separate the yentrieles from the auricles differ both in shape and structure from those that are placed between the ventricles and arteries. The auriculo-ventricular valves are composed of two or more triangular pieces, called cusps, which are attached together at their bases, that is, at the circumference of the opening, but their apices project inwards towards the cavity of the ventricle. The valve between the right auricle and ventricle possesses three cusps — ^it is called Tricuspid (v) ; that between the left auricle and ventricle has only two cusps — ^it is called Bicuspid (y). To the apices and margins of these valves, as well as to their posterior surfaces, strong, yet slender fibrous cords are attached, seen at my m, my m, Figs. 3 and 4 ; the cords by their other extremities being connected to rounded muscular colunms (uy w). Fig. 3, which project from the inner surface of the walls of the ventricles. The valves between the ventricles and arteries (wy z)y Figs. 3 and 4, are both composed of three separate pieces, each piece possessing a crescentic or half-moon shaped form. They are connected by their crescentic margin to the line of junction be- tween the artery and the ventricle, their loose margin aaid hollow surface looking towards the cavity of the artery. Circulation through the Heart. — The circulation of the blood through the heart, with reference to the action of these valves, may now be considered. The blood flows into the right auricle through the mouths of the large veins opening into it, and when this cavity has become distended, its walls contract so as to expel the blood into the right ventricle, the valve between the two being thrown back against the wall of the ventricle, as is seen at Vy Fig. 3, so that the aperture is fuUy open, at the same time the valves guarding tAe orMces of the lower vena cava and coionSkX^ \^\ii a&sist in THE HEABT AKD ABTEBIES. 71 dosing up the months of those tubes, so as to prevent the blood flowing back along them. The superior vena cava, since it does not possess a ralve, permits to a slight extent the regurgitation , of blood. The ventricle, by this means, becomes distended, and, in its turn, contracts, so as to force the blood into the pulmonary artery, the valves at the conunencement of which are thrown backwards against the wall of the artery, w, Fig. 3. In order to prevent the blood at the same time returning into the auricle, the cusps of the right auriculo-ventricular valve are brought together so as to close the orifice, v, Fig. 4. The object of the attachment of the tendinous cords to the posterior surface and margins of the valve, is, that by drawing upon it, they may prevent its being forced too far upwards into the auricular cavity. At the same time that the right auricle is filling, the left auricle also becomes distended by the blood entering it from the pulmonary veins. It then contracts and the blood flows onwards into the left ventricle, which becomes, in its turn, distended. Contraction of its walls then occurs, and the blood is forced into the aorta, and thus throughout the body. During the contrac- tion, the aortic valves (z), Fig. 3, are opened, the left auriculo- ventricular valves, however, being closed (y). Fig. 4, so as to pre- vent the backward flow into the auricles. The object of the valves at the mouths of the two large arteries is to prevent, in that recoil of the arteries which always takes place after their distension by the vent^cular contraction, the backward flow of blood into the ventricles ; for the valves are forced together by the recoil, and thus eflfectually stop the regur- gitation of the blood. This closed condition is represented at w and z, Fig. 4. The alternate distension and contraction of the auricles and ventricles, with the alternate opening and closing of the valves, is continually going on — ^taking place, on an average, about once in every second. The contractiom of the heart ace oxuk^ \sNc\\£D^»rs<^ ^Qs^si^ 73 THE HEART ANS ARTERIES. ^^M is, the will haa no power over them. For the constant mB regular movements of the heart, are of the ulmost importtince in preBerving the life of the individual. If these were Uable to be interrupted or disturbed by the mere exercise of the will, then the life of every person would be placed entirely within his own control — a circumstance which it is wisely ordained should not bethecase. The arteries all proceed, either directly or indirectly, from the right and left ventricles of the heart. The large pulmonary artery, passing from the right ventricle to the longs, will be con- sidered in the chapter on the lungs. The aorta, from the left ventricle, is the great systemic artery, for through it and its nu- merons brauches the blood is carried thronghout the entire system, except that which passes by the pulmonary artery to the lungs, The names given to the arteries for the most part espresn either their position in the body or the parts to which they are distributed. In Pig, 1 a general view is giveu of the dtBtribution of the arteries of the body. An outline view of the bones ia alao given, BO that the position of the artery, with reference to the bone, may be seen. Where a pale tint is given to the arterj', it is in- tended to represent that at that point it hes behmd the bone. The arteries, for the most part, are covered by muscles and fascia ; in very few instances are they placed directly beneath the skin. The Aorta. 1. This vessel springs from the left ventricle of the heart at the upper part of the chest j it extends at first a short distance upwards, and then, changing its direction, passes across the front of the spinal colnran, so aa to form an arch. It then courses down the side and front snrface of the spinal column, as far afi one of the last vertebrse of the loins, thus oc- cupying the cavities of the chest and abdomen, when it divides into two large branches for the lower extremities. At the point of division, a small artery, 2, extends along the Jhjst of the false Fertebrte. In aiuma\& Tposfteasmg & toil, this THE HEAHT AND ARTERIES. 73 branch is considerably enlarged. From the aorta, as from a centre, numerous branches proceed. Thus three large vessels are given off at the upper part of the arch, of which two pasg to the left side of the head and neck and left upper extremity ; the third, very shortly dividing into two, passes to corresponding parts on the right side. As the aorta lies along the different vertebrsB, it gives off numerous branches from its posterior sur- face, of which those found m the chest run outwards, one corre- sponding to the space between each rib, hence called intercostal arteries, 3, 3, etc. The corresponding vessels in the abdomen are the lumbar arteries, 4. From the front of the same large vessel, branches proceed in the chest to the gullet, windpipe, etc., 5 ; much larger ones being given off in the abdomen to the sto- mach, 6, spleen, 7, liver, 8, bowels, 9, and other contents of the cavity. The. artery passing to each arm extends as a large vessel, gradually diminishing in size, as far as the bend of the elbow, where it divides into two branches. It has received different names'in different parts of its course ; thus at 10, 10, it is called Subclavian, from passing under the clavicle ; at 11, 11, it lies in the arm-pit or axilla, and is called axillary ; at 12, 12, when ex- tending down the upper arm, brachial. The two terminal branches of division correspond to the two bones of the fore-arm, and are called radial, 13, 13, and ulnar, 14, 14. The radial, which is placed just beneath the skin and fascia a Kttle above the wrist joint, is the artery commonly selected for fediog the pulse. These two vessels pass to the hand, and form there, by joining.together two arches, a superficial, 15, and a deep 16. From the superficial, branches pass to the fingers, one extend- liig down the sidis of each finger ; they are called digital arteries, 17, 17. At the end of each finger the branches that have passed down its sides join by forming an arch across the front, from -tAich arch many small branches proceed to the skin of the tips Khe Angers. The hand is thus most abundantly supi^lied mtK ^tytibe nnmerouB vessels in it ; ftik \& ^iWfiafc^Xft.^^^^is^"^'^ 74 THE HEART AND ARTERIES. ^sUq^^^l great activity of moTcment, and also with its great sensU Along the whole length of the arteries above named, branches proceed at various ijiterruls, whicli Lave received different names, and which pass to the muscles and other structnreE in the extre- mity. '"" Prom the coramencemeut of the large artery of the arm, a large vessel, the vertebral, 18, extends through a series of holes at the roots of tho transverse processes of the vertebrffi of the neck to the brain, The large arteries, the carotid, 19, 19, extending np each side of the neck, reach uearlj aa far as the angle of the jaw, where they divide into two branches ; of which one, the internal, 20, extends almost directly upwards to the interior of the skull, for the brain; the other, the external, 21, divides into several branches, which proceed to the tongue, teeth, and parts on the outside of the head. The arteries for the face, 22, and temple, 23, are seen. In many persons, espocially in old people, the artery of the temple may be seen ramifying and pulsating beneath the akin. The large artery for the lower extremity, called common iliac, gives off, 24, inner iliac, a considerable siKed vessel, which divides into branches for the parts about the hip. The main vessel continning downwards along the brim of the pelvis, under the name of outer iliac, and along the front and inner surface of the thigh, as the femoral artery, 25, gives off at 26 a large artery, which, by its branches, snppUes the numerous muscles of the thigh ; moat of these extend to the back of the limb to carry blood to the muscles situated there^ The femoral artery then runs to the back of the Hmb, being placed in the ham, 27, at the lower part of which it divides into two branches ; of which one, called anterior tibial, 28, passes through between, the bones to the front of the leg, and then downwards to the npper snrface of the foot ; the other, posterior tibial, 29, con- tinues down the back of the leg to the sole of the foot ; branches proceedlog from the arteries of the sole to eiw^h side of the toes, THE HEART AND ARTERIES. 75 ^constituting the digital arteries. From the large arterial trunks in the leg many branches proceed, to carry blood to the different structures in the limb. Ejrom the Figure, it will be seen that the arteries decrease in size as they pass from the centre towards the circumference of the body. They may be compared to a tree, the main trunk of which is the aorta, whilst the different vessels proceeding from it, either immediately or mediately, are the primary and secondary branches. One large vessel passes to each extremity, extending down the upper part of the limb, and giving off several branches without dhninishing much in size, finally dividing into two branches, which extend along the lower part of the limb, in the upper extremity, to the hand, in the lower, to the foot. These large vessels are placed on the surface of the limb that becomes concave in the act of flexion ; thus the large artery of the ham, in order that it may follow this rule, passes in that space to the back of the limb, for the back of the knee is the concave surface when the joint is bent. This is for the purpose of afford- ing greater protection to the vessels, which, if placed on the convex instead of the concave surface, would not only be more exposed to external injury, but would also be liable to be torn in the movements of the limb. The arteries of the faoe ramify tortuously upon it ; this is for the purpose of accommodating them to the varying size of the face during the elevations and depressions of the lower jaw, over which bone the large arteries of the face proceed. The smaller branches of the arteries communicate with each other, the conmiunication being technically called an an^tomosis ; this is seen in the arches of the palm. It is not confined to this region, but takes place thronghout the body. This is of great importance, for if, through an obstruction in the channel of Que of the arteries, the blood should be prevented going to a part, it would find its way there through the communications which this vessel has with the adjoining ones. The term artery, from a Greek word ^igi^iljm^ wx^ ^^». ^gj^^^ea. 76 THE HEAHT AND AKTER1E8. to these vessels by the ancient Anatomists, because they sap- posed them to contain air. They convey, however, blood. Their cavity has no communication with the exterior of the body, for whilst they terminate by one extremity through their main trunk with the heart, by the other they are connected through the capillaries with the veins. They are cylindrical tubes or pipes, possessing Vails of considerable strength and elasticity, the thickness of the wall and the diameter of the canal in the inte- rior, being regulated by the size of the vesseL Stmotnre of the Arteries. — Several distinct tissues^ make up the wall of the arterial tube. The outer part is composed of fibrous tissue, and upon this the strength of the arterial coat chiefly depends. Beneath this a peculiar tissue, called the yellow or elastic tissue, is seen ; represented in Fig. 5, as considerably magnified. It consists of flattened fibres or bands, which branch at their extremities, at the same time curling upon themselvee. To the presence of this tissue the artery owes its elasticity. The arteries also possess the power of contraction, by which the diameter of the tube can be considerably diminished. Thej derive this property from the presence of involuntary muscular fibres in their walls. These fibres, although possessing the power of contraction, are completely independent of the action of the will. The inner surface of the artery is lined by a perfectly smooth membrane^ which permits the blood to flow along it readily, and without obstruction. This membrane is prolonged into the heart, and lines the whole of the inner surface of the cavities of that oi^ran. The elasticity possessed by the "arteries is of essential service to them« for when the blood is propelled into the aortA by the contraction of the left ventricle of the heart, the coats of the arterv become dilated, in order to accommodate the interior of the tube to the increased quantity of blood forced into it ; for the blood cannot flow off by the capillaries as rapidh^ as It is forwd in bv the heart, JThea the contnctxon of the TmtncV^ c«%s^ no more blood THE HEABT AND ABTEBIES. 77 being forced into the artery, its distended elastic walls recoil and press upon the blood in the interior of the tnbe, a portion of which is at first pressed back towards the heart. This blood passes into the slight hollow between the yalve at the mouth of the artery and the wall of the vessel, and forces the valve back- wards 80 as to close the opening, and thus prevent its further backward flow into the ventricle. The blood has now no course left but to press onwards, and this it does into the capillaries, through which it must pass in order to reach the veins. As the large artery that springs from the heart has to bear the full force of the contraction of the ventricle, it possesses a greater amount of elasticity than any of the other vessels, for which purpose its walls are furnished with a larger quantity of elastic fibres. If the waUs of the arteries, instead of being elastic were rigid and brittle, the pressure thus exercised upon them at such oft- recurring intervals, might cause their rupture. The expansion of the artery, by which it lengthens itself, taking place with each contraction of the ventricle and its subsequent recoil, when it returns to its former calibre, on the termina- tion of the contraction, conditions which occur on an average about once in every second, produce the phenomena of Pulsation, or the Pulse. This takes place in all the arteries of the body. The muscular fibres above described as being found in the wall of the artery, do not by their contraction increase the flow of blood along its canal ; for although they certainly possess the power of diminishing the diameter of the arterial canal, this is merely for the purpose of regulating the amount of blood to proceed to an organ at different times, according to the quantity that it may require. The force of the heart alone is quite suffi- cient to propel the blood along the various arteries into the capil- laries. The Capillaries. — The capillaries are the minute tubes, of the average diameter of 3000th of an inch, extending between the minute extremities of the arteries and veins. They have derived their name from their extreme baic-tik!^ ^ fop the most part closely accompany lY» «c\i^ic\^% % ^'i ^^>isjf^ 1^ 82 THE TEINS. tta Teasel that carrieB blood to the part, as well aa ihe vessel that conveys it from thai pari, lie aide by side. There are cer- tain parts of the bodj, however, where the veins are found with- out anj arteries corresponding to them. This arrangenieDt is especially to be observed in what are called the superficial parts of the body, where a largo number of veins may be seen directly beneath the skin, lying upon the strong membrane or faicia which invests the muaclea and retains them in their proper position. These are called the Superficial Veins. Tliey are re- presented in the figure lying upon the fascia of the left arm and leg. In the other parts of the figure the deep set of veins, or those that accompany the arteries, are seen. Commencing with the right foot, the veins may be traced from the toes, passing over the back of the foot 1, to the leg, where they form two venous trunks 2, corresponding to the anterior tibial artery ; these receive a considerable number of branches in their upward course, which proceed from the great mass of muscles lying on the onter side of the leg. The veins (hat are represented in this leg in the lighter shade of blue, begin in the sole of the foot, and then pass upwards along the inner side of the ancle-joint, as at 3, to reach the back of the leg, along which they ascend 4, closely accompanying the posterior tibial artery, and receiving in their course numerous small veins that proceed from the muscles of the calf of the leg. At the upper part of the leg, the veins on the front pass to the back 5, and, after a short course, join those veins that, aa above described, lie on the back of the limb. The large vein G, formed by the junctioa of these, ascends behind the knee-joint, lying in the space called the ham, along with the large artery of the region. When it reaches the point 7, it leaves this space, and, passing to the in- ner side of the thigh, it ascends, at first on the inner side, and atlerwards on the front of the thigh 8, along with the large artery called femoral, as far as 9, when it passes into the cavity of the abdomen. At the upper part of the thigh it receives the /wj^B vein 10, corre-sponding to the Aec^ artery of the thigh, THE VEINS. 83 which conveys back the blood that has been carried bj that vessel to the numerous large and important muscles of the thigh. Hie femoral vein is also joined at this point bj the large vein called long saphena, 11, formed bj the union of the numerous small veins on the surface of the limb, as seen in the lefl leg of the figure. By the junction of these numerous veins, one large vessel, 9, is formed at the upper part of each thigh, which ascends into the cavity of the abdomen. The veins on the two sides receive in their course the smaller veins which ramify in the lower part of the walls of this cavity, as well as the large vein, 12, corresponding to the artery which conveys the blood to the organs contained in the cavity of the pelvis, and to the parts about the hip-joint. The large veins from each side of the body gradually converge, and, about the level of the last vertebra of the loins, join to form a single large vein, the inferior vena cava 13. The inferior vena cava ascends at the back of the abdominal cavity lying on the right side of the aorta. Several veins open into it, some, 14, proceeding from the walls of the abdomen, others from certain of the organs contained in it, 15. The greater num- ber of the veins proceeding from the organs contained in the cavity of the abdomen do not open directly into the vena cava, but form a large vein called portal^ which will be afterwards more particularly described. The vein then, at 1 6, passes through the diaphragm, enters the cavity of the chest, and terminates by opening into the right auricle of the heart. It is cut across in this figure just before its termination; its entrance into the heart may, however, be seen at h, figs. 2 and 3, in the representations of the heart. Passing now to the deep veins of the right arm, it will be seen that they commence at the tips of the fingers, that they pass up the sides of the fingers to the palm of the hand, where they form an arch, 17, corresponding to the artjBrial arch of the palm; from this theys extend upwards along the front of the fore arm, 18, as far as the bend of the elbow, closely accompanying iVva ^T\Kt\«a» of the fore arm, and receiving from the m\x^e\ea Ti\SL\£i'etw5& ^\si"5i^ S4 THE TEIire. branches corresponding to the small arteries sent to those mus- cles. At the hcnd of the elbow, two veins result from the junc- tion of these different veins of the fore arm, which pnas up the inner side of the npper arm, ID, closely accompanying the bra- chial artery as far us the armpit, where they join to form a single large vein, the Bjcillary, 20. They receive in their course mauy small branches from the muscles. The axillary vein receives, at 21 and 22, two largo veins formed by the union of the numerous small superficial veins of the arm, seen in the opposite limb. Thus, in the upper as well as in the lower extremity, a single large trunk conveys nway al! the blood that has been circulating through the limb. This largo vein passes beneath the collar- bone, reaches the lower part of the side of the neck, 23, where it is joined by the large veins that return the blood iVom the head and neck. The veins tluit return the blood from the inner and outer parU of the head and neck are called the jugular veins, inner 24, and outer 25. Of these, the outer is the smaller. It may commonly bo seen beneath the skin on the side of the neck. It returns the blood that has been circulating on the outer part of the head, 2G ; hence it must be regai'ded as a superficial vein, and must consequently be placed in the same category as the superficial veins of the limbs. The iniernal jugular returns the blood that has been circulating on the face 27, in the brain, and in the deeper parts of the neck. It accompanies the carotid artery, and must thus be regarded as a deep vein. By the junction of these large veins at the root of the neck, a much larger vein on each side is formed. These gradually con- verge so as to form u single trunk, the superior vena cava, 20, The superior cava is placed at the upper part of the cavity of the chest, and to the right aide of the first portion of the large artery called aorta. After a short course, it enters the upper part of the right auricle of the heart, as may be seen at g, figs. 3 and J, in 7 the representations of the heart. TJie veins corresponding to the intetcoatal arteries, that run THE VEINS. 85 between the ribs, do not open into either the superior or inferior vena cava, but pass to form a vein of considerable size which lies upon the vertebrse of the chest. This vein is called the azjgos vein. It begins in the cavity of the abdomen, 30, 30, then enters the cavity of the chest, and, as it courses upwards, gradually in- creases in size by receiving the various intercostal veins, until it finally terminates, 31, by joining the superior vena cava. Turning now to the extremities of the left side, the arrange- ment of the superficial veins may be examined. These are separated from the deep veins by the strong fascia binding down the muscles. They commence by very fine branches arising from the capillaries of the skin. If the back of the foot is ex- amined, it will be seen that the veins proceeding from the skin of the toes form an arch, from the inner side of which a vein, 11, proceeds, called long saphena. This passes upwards along the inner side of the leg and thigh, increasing considerably in size in its course, owing to the number of branches joining it from the extensive surface of the skin of the limb. It terminates, as already mentioned, at the upper part of the thigh, by passing through a bole in the fascia, and joining the femoral. The superficial veins of the hand commence at the tips and sides of the fingers, from which they proceed along the back of the hand, beneath the skin of which they may be distinctly seen. They then ascend along the fore arm, forming three large veins: the radial, 32, on the outer side ; the ulnar, 33, on the inner ; and the median, 34, in the middle. At the bend of the elbow, the median divides into two branches, of which one joins the radial, to form the cephalic, 22; the other joins the ulnar to form the basilic, 21. Into one or other of the two branches of the median the surgeon generally makes an opening when he is de- sirous of drawing blood from the patient. The cephalic and basilic veins terminate by joining the deep or axillary vein, 20. The communications between the superficial and deep veins are not, however, confined to the point of tenIi\uat\Q\iQl^^3GL^l^^\ss5S(^ but occur at various parts of their couise, «& «X ^^* L 8G THE TEINS. From t!ie ilescripLion that has now been giveu of the a und veins, it will be seen ibat the wliole of tlie body is traversed by two distinct eeta of tubes or vessels. The one, the arleries, commencing at the left ventricle of the heart as a centre, by a large vessel, the aorta, which gives oS from its sides large branches — these in their turn giving ofi* other branches, — the tubes, by tliis means, beconiing smaller and smaller until they finally terminate in the minute hair-like fessele, the capillaries. The veins all commence in the capillaries as small vessels, which gradually unite together, so as to form larger and larger veseela, until finally, as they approach the heart, two large veins only are found, which terminate by opening into the right auricle of the heai't. Strnctme of the Veins. — The veins, bo far as their general structure is concerned, correspond closely with the arteries. walls are, however, thinner. They possess, like the i, a smooth membmne lining their interior for the purpose of allowing tlie blood to flow easily along them. They difier from the arteries, however, in one important particular, viz., in the possession of valves. Fig. 2 is an enlarged view of a vein cut open throughout the greater part of its extent, in order to exhibit the valves in the interior. These are generally arranged in pairs, as at a, a. The divisions of the valve are creacentic, or half-moon shaped; of tlieir two margins, one, b, is attached to the wall of the vein ; the other, c, lies loose in the cavity of the vein : of their two surfaces, one, d, looks towards the cavity of the vein j the other, e, looks to the wall of the vein, — between thia latter surface and the wall of the vein is a small pouch into which the blood can pass. The valves may be situated either in the course of a vein, a a, or at the point of junction of a small with a large vein,// Uses of the Valves. — The valves are so placed as (o allow the blood to How freely along the veins to the heart, but they efiec' titaiJj' prevent the blood from flowing back again. Numerous coaunuDicatioBs, or anastomoses, take p\BK« \wi<.'«eeu "iW ^aS;.i:«tit TUB VEINS. veins lying in the Bame part of (he body, not only of the deep v«iiis with each other, and the euperficial veins with each other, but also of the deep with tlie superlicial veins. These anasto- moses, owing to the valves that are so generally placed at the point of coram UDicBtion, exercise most importiuit iofluences upon the passage of the blood through these vessels. The valves are most abunilaiit in the veins of those parts of the body where the circuiaiion is likely to be interfei-ed with by the action of the muscles, and by the pressure of the blood induced by its gravity. It is in the same pai-ts also that the superficial veins are found. When the muscles contract during the movements of a pari, they naturally press, to a certain extent, upon the veins running between them. This pressure, according to the laws regulating the motion of fiuids, would have a ten- dency to force the blood partly forwards towards the heart, and partly backwards towards the capillaries. The backward move- ment would, of necessity, retard the circulation if allowed to go on, but as soon as the blood reaches the first pair of valves, it passes into the pouch, e, between the valve andlhe wall of the vein, forces the valves together, and thus completely prevents any further regurgitation. Tha blood has now to seek some other channel, by means of which it may pursue its course to the heart. This it finds in the communicating brunches which connect the deep and superficial set of veins, along the latter of which it now passes; for these veins being separated from the muscles by a strong fascia, are necessarily not subjected to the same pressure aa the deep veins. Hence this double airangemeot of veins in a part is for the purpose of affording a collateral channel, along which the blood may pass to the heart during the the muscles of the part. Thus, during continuou, superficial veins always become distended with blood, so that their outline may be readily seen beneath the skin. The extremities being the parts where the muscular move- menta are most violent, are most abundantly ^covvd^'wS.V'a.' een^^^ 1 i!8 THE VEINS. Movements of the Blood. — Along the vessels wlose aiTonge- ment has now been described the blood is continually flowing. Numerous experiments show tliat the contraclioti of the left rentricle nlone is productive of an amount of force Bulficient to propel the blood through the arteries into the capillaries, through these into the veins, and so back to the right aide of the heart It has already been shown that, owing to a larger amount of blood being forced into the arteries than can at once pass through the capillaries, a certain amount of the heart's nctiou is expended in dilating the arteries. But as these vessels, by their recoil, assist io pressing on the arterial blood (its backward movement being restrained fay the closure of the valves at the commence- ment of the aorta), it may be considered that the whole force of the ventricle is thus employed in urging on that fluid. The pressure exercised by the recoil of the arteries, taking place at a time when the ventricle has ceased to contract, and when, consequently, the blood has not the benefit of any direct force derived from this coutractioo, assists in a most material manner in its propulsion. The pulse, which is produced by tho alternate distension and recoil of the artery, thus affords an accurate guide to the number of the contractions of t!ie heart ; every beat of the pulse indicBt- ing a contraction of the ventricles. It has been stated that the healthy average number of pulses, or ventricular contractions, are about 60 in the minute, or one in every second ; but the number is often found somewhat to exceed this, and, in certain instances, to eacced it considerably, the health at the same time being quite good. Considerable differences in the number of pulsations in the minute are obserrcd at different periods of life. In children they are much more fre- quent than in the adult. The position of the body also exercises a great iniluence upon the pulse ; the heats being more numerous io the same person when standing than when silting, and when sitting than witen lying down. THE VEINS. 89 The pulse cannot be felt in the very smallest arteries, in the capillaries and veins ; for the blood flows through these with a continuous onward movement. As the blood passes through the capillaries certain changes take place in it, consequent upon the attraction subsisting be- tween some of its constituents and the structures lying on the exterior of these vessels. This attraction is supposed by many physiolo^ts to assist, to some extent, in the circulation ; but as a consideration of this question involves an inquiry into the phy- siology of nutrition, it had better be reserved for the present. That the blood circulates or moves throughout the vessels, is a fact which has now for upwards of two centuries been recognised by anatomists. The fact of its doing so was first announced by ECarvey in 1619. He was led to this conclusion by observing the continuous arrangement of tubes in which it is placed, and the valves placed at the origins of the arteries from the heart, between the cavities of the heart, and in the interior of the veins ; the valves being so connected to the walls of the vessels, that while they afford every facility for allowing the blood to flow freely onwards, yet they put a most effectual bar to its backward movement. The close similarity, also, between the muscular structure of the heart and the other muscles of the body, indi- cated the source whence the motor power that impelled the blood was derived. The improvements that have taken place of late years in the modes of conducting anatomical investigations have supplied anatomists with another proof of the circulation of the blood ; for, by placing a transparent animal structure, such as the web of a frog's foot, or the wing of a bat, beneath the microscope when the animal is living, the particles of blood can be readily seen moving in the small vessels of the part. TU£ BLOOD. CHAPTEE vin. THE BLOOD. E blood is the important fluid which circulates tbi'ougka entire body in the various tubes or vessels which have been described under the names of arleriea, capillaries, and veioa. It is the most important of the animal fluida ; for it conve)-a to the various textures the materials by means of which they may make good the waste continually taking place in them from exercise or decay, and it also removes from these textures certfun waste products formed in them during their employment and use. When drawn from the body during life, itflowsout aaaredfluid, which, if it proceeds from an artery, has a mucb brighter colour than if it proceeds from a vein. In either case, if received into a cup or other vessel, certain changes soon commence to take place in it. In a few minutes, it begins to thicken, and very shortly sepa- rates into two distinct parts — a solid red portion called the clot, and a fluid portion, of a light yellow hue, the serum. This change is called the coagulation, or clotting of the blood. The exact period elapsing between its being drawn from the body and its coagula- tion varies much in different instances. It seems to be facilitated by exposure to the air and agitation ; circumstances which favour the evolution of a small quantity of ammonia from it, as has been lately determined by the experiments of Dr Richardson. The chemical composition of the clot and serum present remarkable difierences. The clot consists of a material called fibrine, and of myriads of minute circular bodies called the corpuscles or globules of the The fibrine is the constituent of the blood upon which its ■ulability depends. So long as the blood is circulating in the the S.br'mei remains in BolutVoa-, \iiiv \v ^vi.%«.?fte& the THE BLOOD, remarkable property of Bolidifying imuediatelj afler it is drawa^ &om the body. During ita BoHdiScation it forms a number of rerj fine threads, vfaich entaDgle in their meshes the corpuscles of the blood, upoB the presence of which the rod colour of the clot depends. The eorpuscles are figured in Plale IV., Fig. 7. These corpuscles are extremely minute bodies. In order to see tbem, a very high magnifying power must be employed, for tbey are not more than x^ai;th of on inch in di&meter. In their ehape tbey have been compared to small pieces of coin ; their surfaces, however, instead of b^ng fiat, are in soma ioslsnces concave, in others convex. Two kinds of corpuscles may be distinguished, the red and tb» white; the former are by far the most abundant. * The red corpuscles possess a remai-kable compoMtion — tbt metal, iron, most probably combined with oxygen, playing a most important part in their constitution. The serum of the blood consists of water holding in aolution the other constituents of the blood. These are both numerous and diverse in their composition. For na tbe blood is the only Boarce through which tbe tissues can receive tbe materials from which they are formed, it follows that the blood must contain these difierent substances. Certain of the waste materials of tbe body are also found ip it. These are all dissolved in the serum. The contents of the serum may thus be divided into building materials and waste products. The most important of the for- mer is the substance called albumen ; a compound which, in its pr^erties, resembles tbe white of an egg. Numertjus inorganic substances, chiefly in the form of salts, are also found dissolved in it ; amongst tbe most remarkable of which is common salt, together with compounds of phosphoric acid, with potash, soda, lime, and magnesia. One of the most remarkable of the waste products in the blood is sugar ; but as this, together with the class to which it belongs, is on its way to be separated Ei:om.\,'Qfe\nA-iVv\. never aecumuhtea, in healthy blood at \ea8l, Vs Mi-j ^ea.\.«.iA».'«^- 1 IB ^^ ■HUE BLOOD. ^r^H The blood also contaiiis a small quantity of Hitt.y matter i solved in it. The peculiar odour of llie blood is due to one of its fatty constitucnla. This odour is bo characteristic, that it enablea those accualomed to discrimiuate in such niattera lo distinguish the blood of one animal from that of anotlier, A certain variety, a^ regards quantity, amongst all the consti- tuents of the blood, is quite compatible, however, with a healthy state of the system. This variety depends partly upon the nature of the food, partly upon the age, and partly upon the temperament of the individual. The blood of those who feed exclusively upon animal or vegetable food is found to possew certain differences. Under an animal diet, the solid constituents of the blood are more numerous than under a vegetable diet; the increase especially taking place in the quantity of the cor- puscles. If the blood is examined shortly aft«r taking a meal in which there has been a considerable quantity of fat, it presents a slightly turbid appearance, owing to the presence of fat in a minutely divided state. The amount of sugar in the blood is also found to be increased ailer a quantity of it has been eaten. The red corpuscles are more numerous in the blood during the prime of life than in childhood or old age, and they are also more nbaudant in the blood of men than of women. These facts, bearing upon the amount of the corpuscles at tlie different periods of life, and in the two sexes, would appear to afford a clue to their pecu- liar use. It is probable that they are the especial source of the materials from which the muscles and nerves are formed, parts of i the body which are so much more vigorous in the adult than in any other period of life, and in man than in woman. That diseased state of the blood, which is called poor blood, and which is conse-j quent upon great diminution in the number of the red corpuscles, is always accompanied by considerable bodily and mental debili^. The albumen appears to be the material from which Ihe blood- corpuscles are moat probably formed ; and thus, through the medium of these bodies, it assists in building up some of the niost important tissues. THE BLOOD. The fat of the boJ/is derived from the fatty particles foum blood. The sugar, and other waste products, are on their way tol be separated from the blood cither by the lungs, kidneys, or skin^r The inorganic constituents of the blood — and by this te merely the salts of the blood, but also the iron of the corpusclesi I is included — although bearing a amall proportion to the albumen, I fibrine, and organic part of the corpuscles, yet exercise a most J important part in the economy of the body. For the whole o the solid parts of the body contain certain of these substances, iai greater or leas proportion. In the nerves, muscles, tendons, ligaments, they are in much less abundance than in the bones and teeth. The blood is the channel by which they are coD' veyed to these tissues. Certain of the tissues appear to have a. preference for certain of these substances. TJius the bones ami ^| teetk -contain much larger quantities of lime, combined with ^| phosphoric acid, than of any other inorganic constituent. The ^1 different parts of the nervous system conlaiu sails of phoaphorie acid. The muscles and hair possess peculiar attractions for the iron of the blood. The muscles a!so contain a considerable pro- portion of the salts of potash. Upon the phosphate and carbo- nate of Boda the chemical reaction or alkalinity of the blood is most probiibly due — a most important property of the blood — for it is upon this that its fluidity to some extent depends. It is somewtiat difficult to form an opinion of the use of the common salt, although it is iho most abundant of all the salts of the ^ blood. It is the most generally diffused of tlie inorganic consti- ^| tuents, for it is found, in greater or less abundance, in all ths^| tissues of the body. The various structures of the body, thua ' having affinities or attractions for certain constituents of the blood, possess the power of selecting from the blood, as it passes through the fine capillary vessels lying amongst them, those par- ticular constituents for which they have a special attraction. So long as those different substances are in a proper quantity and quality in the blood, and so long as the tissues are in e, lv«a.\t.Wj Etate to select them from the blood, the syatenx VvX^^iQ -^TOS^xve.^ 94 THE BLOOD. in a stale of health. It is in these localities also that the waste products already mentioned find tiieir way into the blood. The blood, in addition to the various solid constituents already described, has certain gases dissolved in it. These are oxygen, carbonic acid, and nitrogen : of these, the two former are the most important. Certain differences are observed between the amount of oxygen and carbonic acid in blood drawn from an artery and a vein. In arterial blood there is more oxygen and less carbonic acid than in venous blood. The difference depends upon this circumstance — that as the blood passes through the lungs, it absorbs from the air lying in the lungs a tjuantity of osygen. This is carried by the blood flowing along the arteries to the capillaries. Here, in consequence of the changes taking place, the blood parts with a quantity of its oxygen to the tissues, and receives fi'om them a quantity of carbonic acid, which is formed by the action of the oxygen of the blood upon the carbon of the tissues. The venous blood which now flows froni tlis capillaries is thus charged witli carbonic acid, which it conv^ to the lungs. In the lungs, the blood parts with its carbonic add to the air, and receives osygen from it. The venous blood, by this means, becomes reconverted into arterial. The cause of the difference between the colour of venoin and arterial blood has been variously stated by phydolo^sts. Some supposing that it depends upon the corpuscles in the two kinds of blood possessing different shapes, so that they reflect light differently. Others, and this appears to be the most probabls opinion, regard it as due to a chemical difference between tiifl action of the oxygen on the corpuscles iii arterial, and the car- bonic acid on the corpuscles in venous blood. The quantity of blood in the human body varies very much in different individuals. It appears, however, to bear a TtiMint proportion to the weight of the body. It has been estimMed that the weight of the blood is to the weight of the body as I to 8; — so that, in a person weighing IGO lbs., the blood would wc/fffi 20 lbs. THE LUNGS AND BESPUUTION. 95 CHAPTER IX. THE LUNGS AND RESPIRATION, In the previous section^ it has been seen that the blood receives from the tissues^ as it passes through the capillaries, certain waste 'products, which require to be excreted or separated from it. Amongst the most important of these is carbonic acid gas. This gas is separated from the blood in the lungs. The process by means of which this separation is effected is called the func- tion of respiration. The lungs are the organs in which this function of respiration takes place. In Fig. 3 the front of the chest has been removed, so as to give a view of the position of the lungs. The lungs, a a, are two in number, one being placed on each side of the chest. They are separated from each other bj the heart, and great vessels con- nected to it, which lie between them. They are conical in their shape, resting by their bases on the upper surface of the large nrasde called diaphragm, b b, which separates the chest from the abdomen. Their apices project upwards to the root of the neck. Their outer surface is in close contact with the inner surface of the wall of the chest. The exterior of the lung is covered by a perfectly smooth and glistening membrane, called pleura, which is also prolonged over the inner surface of the wall of the cavity in which the lungs lie. The perfect smoothness of the opposing surfaces of this membrane enables the lungs to move freely within the cavity of the chest, without sustaining, during respiration, any injurious effects. In order to understand the mechanism by means of which the venous blood is purified from the carbonic acid it contains, the arrangement of the air-tubes and blood-vessels in the l\iw^ \s^x^&x» next be examined. 06 THE LUNGS AND BESriHATIOJt; Fig. 4 gives a view of the air-tube, winj-pipe, or trachea, e. Thia is continuous by its upper end with the larynx, d^ through whicU it opena into the back of the mouth. From this part it pasBes downwards into the cavity of the clieat, and divides at e into two large branches, called bronchial tvhee,f, f, one for each lung. Theae enter their respective lungs, and then divide and sub-divide into smaller and amaller branches, aa may be seen in tli8 figure. The different divisions of the air-tube are kept per- manently open, owing to their walls containing, at intervals, rings or plates, g g, q( a, gristly elastic material, called cartilage, which effectually prevents the aides falling together. Thus an open passage is always provided for the upward and downward movement of the air. If any one of tho small branches of the air-tuhe, as h, be followed out to its termination and highly mag- nified, as in A, Fig. 5, it will he seen to terminate by a closed end. But, before its termination, the walls of the tube became extremely thin and transparent, and dilate into a number of small pouches, called air-cellt, j, each of which communicates with the interior of the tube. Looking again at Fig. 3, it will be seen that a slice has been removed from the front of the left lung, so as to eshihit the course of Ibc bronchial tubes, f, in it. Closely accompanying these tubes are the branches of the large artery called pulmonary, i, which springs from the right ventricle of the heart. In Fig. 5, one of the branches of this vessel is shown running by the side of the bronchial tube, and, as that dilates into its pouch-like termination, the pulmonary artery divides into a great number of very small capillaries, k, which form a close and minute network on the outside of the pouches. From this net- work the rootlets of the pulmonary vein, x, arise, which join together so as to form the large pulmonary veins which enter the lell: auricle of the heart. Throughout the whole of the sah- stance of the lunga, the pulmonary vessels and air-tubes are dis- tributed in the manner now described ; tho substance of the k being; in /act, made up of the diviaiona ot ^\\caA ^osaek. M THE LUNGS AKD KESPIBATION. Hovements of Respiration. — Such being the stractures e plowed in tUe purification of the blood, it will be advisable, i the next place, to coneider the movemcnlfi, by means of whidj the air and blood are brought into contact with each other, this purpose, a somewhat complex upparutus is provided. The movements of respiration are divided into two kinda- one, that of Inspiration, when nir ia drawn into the lungs waUa of the chest being elevated, and its capaGil7 increased ; the other, that of Expiration, where the air is expelled from the lungs, the walls of the chest depressed, and its cavity dimiuished. By referring to Plate I,, Fig. 1, it will be seen that the walla of the chest are formed by the ribs, which are attached in front, through their cartil^es, z, to the breast- bone, whilst behind they are connected to the vertebrie of the chest, a moveable joint exist* ing at each extremity. Occupying the spaces between each of the ribs are two muscles, called intereoatal miieeles, one placed outside the other, which are cot seen in the muscular figure, because they lie beneath the great muscle of the chest. Portions of these muscles are represented in Plate V., Fig. 3, m. Connected with the first and second ribs, on each side, are two muscles called lealene, n n, which extend upwards to be attached to the transverse processes of the vertebra of the neck. In order (o produce an ordinary inspiration, the outer interco tal muscle in each apace contracts, and by this means the two ri to which it is connected are elevated, the space between the ri being at the same time increased. These muscles are not, how- ever, the only agents by moans of which the elevation of the ribs is performed ; fur there are certain small muscles connected to ti ribs behind, called elevators of tke ribs, which greatly assist. ' scalene muscles also, n n, which represent in the neck the tora of the ribs, raise especially the first and second ribs, in ing thereby the diameter of that part of the cheat in which the apex of the lung lies. By this means, the diameter of the cheat IB increased from side to side. The elevation of the rilw ^t.'i same time tltitisCs forwards ths breast-bonB^ 'w^iu^'ub'^ec^^ how- to i^^^hJ elevj^H ch the L 98 TOE LrNGa and respibation. able, and, to a sliglil extent, also Ibrusts Imckwards tbe vertebrae of the chest, so that the thoracic cavity sustains an increaae in its diameter from before backwards. This is not all ; for through the agency of the large muscle, the diaphragm, b b, the diameter is also increased in the direction from above downwards. This muscle, when in the relaxed condition, os represented in the figure, arches high up into tbe chest, so that its upper surface is very convex ; but when it contracts, its fibres straighten, so that ihe muscle becomes much more flat, and tlius affords in- creased space for the lungs in the lower part of the chest. Through these different agents, the chest expands in all its dia- meters. As this takes place, the lungs at the same time expand, by tbe air rushing into them, so that they remain closely in con- tact with the inner surface of tbe wall of tbe chest. In this man- ner is produced tbe movement of ordinary inspiration. When a more violent inspiratory effort is required to be made, other muscles are called into play to assist in ibe eleva- tion of the ribs. The head, the spine, and the shoulder-boneS become fixed, in order to allow certain muscles passing from them to tbe ribs to draw upon the ribs, and thus increase the diameter of tbe cavity. When the inspiratory movement bas ceased, that of expiration begins. The walls of the chest, which are highly elastic, recoil, and at the same time press upon the lungs, so as to expel from them the air which bad ruBbed in during the inspiratory effort. The recoil of the thoracic walls is also assisted by the action of certain muscles, such as the inner layerof the intercostal muscles, which, by drawing down the ribs, assist in the expulsion of tbe air. Expiration must, however, be regarded as essentially per- formed by the recoil of an elastic structure previously distended ; receiving comparatively little aid from any muscular arrange- ments. These two movementsalternate with each other during life, from 16 to 20 occurring every minute during the state of health. The interior of the tur-passages, along which the !ur passes ta tbme movementB of respiration, ia Unei \s^ e. membrane, which J THE LUNGS AND KE8PIKATI0JJ. Dr Hulchinson has sh to make a deep inspiriiti exerted, in order to chest, and the atmOBph< froQi its forming & moist and somewhat slimy secretion, has been called a mucova membrane. The surface of this membrane covered hy an immense number of the minute bodies, repre- sented in fig. 6, magnified about 500 times. Projecting from their broader ends are the fine hair-Hke bodies, cilia, a, as they are called, which are continually moving in a direction away from the lungs towards the mouth. Their supposed use is to facilitate the passage upwards of the slimy material which constantly in process of formation by the bronchial muci membrane. n, by his experiments, that, in oi , the amount of muscular force tc J the eiasticity of the walls of c pressure upon the surface of the ch< is equal to rsiising a weight of 1000 lbs. The movements of respiration belong to that class of ments which is termed automatic ; — that is, they go on as i mechanically, witliout there being any necessity for the will determine that they shall take place. Tet, though essentially' automatic, the will has to a certainextent power over them. Thus, it Is quite possible to suspend the respiration for a few seconds; but very shortly the necessity of breathing manifests itself, and the respiratory efibrta must again be commenoeiJ. If, through any cause, the breathing be suspended for a few minutes, death iDOSt certainly takes place. Various famihar actions are only modifications of the ti movements of respiration. Thus sighing consists of a long ani forcibly drawn inspiration ; whilst coughing is a forcible expii tioD, for the purpose of expelling some obnoxious material fi the lungs or bronchial tubes. Certain differences may be observed in the movements the chest in the two sexes. In adult males, the lower pt of the chest is more moveable than the upper ; the being the cose in adult females. Aa the function of reapiralion can only be ^to\>«i\^ iiWK\«&.J aen^^H 100 -niB LUNoa and kebpiratiox. 1 by Eillowiiig perfect freedom of moTement to the walls e chest, it must be obvioaa that, in the arrasgemeDt of the dress, no means should be adopted to cramp or restrain the moTenieiitB of the ivallB of this important cavity ; for the amount of air that can be inspired and expired does not entirely depend upon the capacity or size of the chest, but is apparently greatly influ- enced by the mobility of its walls. The name of vi/al capacity has been employed to express the amount of air that can be expelled from the lungs by a forcible expiration, after making the fullest inspiration. The height of the individual has been found to bear a very striking relation to this vital capacity. The average qiianlity of air that can be ex- pelled by an adult male of five feet in height being 174 cubic inches, which may be regarded its his vital capacity. For every inch of stature above this, eight cubic inches In addition can be expired. So that an individual six feet in height would expire 262 cubic inches. However forcible an expiration is made, the whole of the air is not expelled from the lungs, a certain quan- tity always remaining in them. This has been called residual air, and it is in this that the interchanges between the blood fttid the air take place, which we will now consider. Changes in the Air and Blood during Respiration. — The air or atmosphere is composed of a mixture of the two gases, oxygen and nitrogen, with a very minute proportion of carbonic aoid) and a variable quantity of watery vapour, dependent upon the moiaturo or dryness of the atmosphere. The venous blood, as it flows along the small capillaries of the pulmonary artery, contains a laro« quantity of carbonic acid gaa dissolved in it. This blood be m sp s d o the action of the air lying in the air-cells ; he a a d b od being simply separated from each other by he h n ra parent membrane forming the walls of the capil! n and h a -cells. An inter- change now takes place betwe n he a o the blood and the air in the cells. The carbonic acid passes out of the venouB blood, tbroagb the moist peTmeci.bVfi mmb^aiv^a ^^iiaui^ the THE LONGS AND EE9PIHATION. H walls or the tubes, into the air-cells ; whilst the oxygen of the au^< passing in the opposite direction through the same porous meni- bnmes, enters the blood ; the membranous walls of these tubes, owing to their extreme thinness nnd permeability, offering no obstruction to this interchange of the gases. The blood now flows into the pulmonary reins, having parled, whilst passing Uirough the pulmonary capiJlftriee, with its carbonic acid, and having received a considerable amount of oxygen ; the change in its colour from dark purple to bright scarlet — that ia, from Tenons to arterial blood, at the same time occurring. The vessels of the lungs thus furnish an exception lo the general statement, formerly made, that arteries conveyed arterial or pure blood, and that veins conveyed venous or impure blood ; for, as has now been shown, the pulmonary artery contains Tenoiu blood, whilst the pulmonary vein contains arterial. The blood also parts with a varying quantity of water in the form of vapour, the proportion depending upon the amount previously contained in the inspired air. The air, having lost a large proportion of oxygen, has acquired a considerable acces- sion of carbonic acid and watery vapour, and in this form it is expired. That such substances are contained in very evident quantities in expired air, may be readily shown by a simple experiment. If a glass, containing perfectly cold lime-water, be taken into a room in which a number of persons have been for some time assem- bled, in a few minutes a quantity of moisture will condense in drops upon the oulside of the cold glass, and the lime-water it contains will become quite milky from the formation of carbo- nate of lime. In this manner, during every expiratory effort there is evolved from the lungs a quantity of carbonic acid — a gaa which possesses noxious and even poisonous properties. From the lungs of a large mass of persons assembled in a room, the amount of carbonic acid ezlialed into the atmosphi great ; and, in a short time, unless means be taken to ei tbroitgh proper ventilation, the entrutca ol «. f^c;^ tn.^-^. ^^^ THE LDNGS AND RESPIRATIOIT. rettCT ', and iha exit of the impure, tlie atraosplierc of the aci^nirea verjr deleterious prtipertieB. This maaireBts itself bj producing in most persons fainting, and a general feeling of diB- comfort. If this is allowed to go on, death would ultimately ensue — an instance of which is afforded in the well-known ac- count of the Black Hole of Calcutta, in which a number of peraons were confined in a amall room, during the night, with- out any fresh air being allowed to enter, when, out of 146 who were put in alive, 123 died. The crowding togeliier of a num- ber of persons in a confined space is thus to be most carefully Avoided, unless means are taken at the same time to ensure a continuous influx of fresh air. The carbonic acid produces its poisonous ofl'ects, partly through its directly injurious action upon the system, and partly through the inspired air containing it possessing a smaller proportion of oxygen than is necessary for the continuance of human life. The blood, in these instances, be- comes highly charged with carbonio acid, so that it esercisea a most depressing intlueuce upon the brain and other parts of the nervous system. The nitrogen gas contained in the atmosphere plays but a very secondary part in the function of respiration. It appears simply to fulfil the purpose of diluting the oxygen, which< as has been frequently shown experimentally, if inspired pure, produces great and injurious excitement. The quantity of air passing through the lungs of a healthy adult during the day has been estimated at between 300 and 400 cubic feet ; and it baa been calculated that, in providing accommodation in rooms ihnt are to be inliabited, at least 800 cubic feet should be Mt apart for each person. Diftgram of the Circulation. — By the aid of Fig. 7, a ccm- plete view of the circulation of the blood in the human body may now bo obtained. This figure is merely to bo considered as a diagram constructed for the purpose of giving as simple an idea as possible of the course of the circulation. Tie reaous blood is collected from Oite hQ%d e-nd neck, i ANIMAL HEAT. 103 and extremities, by the rootlets of the great venae cavee, g and hj and through these veins it is poured into the right auricle of the heart, d; from this it flows into the right ventricle, 6, which pro- pels it through the pulmonary artery, t^ into the lungs. Here it parts with its carbonic acid and receives oxygen, having become converted into arterial blood. It then enters the pulmonary veins, k and 0^ and flows from the lungs into the left auricle, e, and from this into the left ventricle, c. By this it is propelled into the aorta, /, and through this vessel and its numerous branches throughout the whole body, to be returned to the heart again through the general venous system. That part of the blood which flows to the stomach and intestines, n, through their arteries represented by m, does not pass at once into the general venous system,- but enters, by a distinct vein, called ported vem^ Oj the liver, p^ through which it passes before entering the vena cava through the hepatic vein, q. CHAPTER X. ANIMAL HEAT. In connection with the subject of respiration, it may not be uninteresting to inquire how the heat of the body is produced and maintained. It is a fact that is now well ascertained, that in whatever localities the healthy human body is placed, whe- ther exposed to all the cold of an arctic winter, or the intense heat of a tropical sun, it preserves, so far at least as regards the heat of the interior, an almost uniform rate of temperature. The heat of the surface of the body, especially that of the extremities, varies, however, greatly, according to the tempera- ture of the external atmosphere. This uniform temperature of tlio inleinot o^ VXi^ V\«aas!L\s!^^ 104 AMIUALH^IAT. is essential to the proper carrying on of the functions 1 Bary to life. Id order that no estraneotia cause may interfere with these functions, the body perfomis within itself the processes essential to the generation and preservation of the proper amount of heat. This power is not merely possessed by man, but is shared by all other mmnmalia and birds. Hence, ihey are all classed together under the name of ivarm-blooded. Fiahea and reptiles, on the other hand, have their temperatures greatly infJuenced by (he medium in which they live. This is, as a rule, lower than the temperature of man, so that they feel cold when touched. Hence they are called cold-blooded. The average temperature of the interior of the body of man — say, for instance, the inside of the moulh — deduced from a great number of observations, is 100°. This temperature is derived from a low combiiation, which is continually taking place throughout the whole system during life. The oxygen entering into the blood at every inspiration, as it passes through the capillaries, combining with certain of the constituents of the tissues, in order to form new and more simple compounds, — the most important of these combinations being with carbon to form carbonic acid, and with hydrogen to form water, — compounds which, we have already seen, are separated from the btood at every expiration by the lungs. It was formerly supposed that the union of the oxygen with the carbon and hydrogen took place in the lungs alone. If this had been the case, the temperature of the lungs would have been much higher than that of the other internal parts of the body, which is not so. Chemists have long recognised the fact, that chemical cora- hiaation, whether taking place externally or in the interior of the body, always produces heat. By accurately calculating the t of oxygon inspired during a given period, and the it of carbonic acid expired during the same period, it has been esdmated that the extent of chemical combination taking place during that time is nearly Bufficienl \o \iTiid\ia« the neces- ANIMAL HKAT. 105 f Btnoant of heat, — tlie balance being made up b; the hea^l generated in the combination of oxygen with hydrogen to foroi f The nervous system is fonnd to exercise considerable influ- ence upon the generation of heat ; for if the nerves going to a port be divided, the temperature of that pari falls, from which some physiologists have supposed that the nervous system posseeses tlie power of producing heat. This diminution of temperature may be explained, however, by the circumstance that the nutritive changes, which result in the combination of oxygen with the other elements, are much less efficiently per- formed when the nerves are divided or injured than when they are entire. Hence the amount of chemical combination taking ^oce, Mid consequently the amount of heat produced, is not 80 i great. The function of respiration must thus be regarded aa subor- | dinate to the employment of oxygon, and to the production of 'j carbonic acid in the interior of the body — that is, to the combus- [ tlon which CDnstitutcs an essential part of the pro natricion. In a previous section, we have spoken of the blood containing J fatty matters and sugar in solution. These materials play, to some extent at least, the part of the fuel, by the combustion of which the animal heat is generated ; for tlie oxygen contained in the arterial blood combines with the carhon and hydrogen of which these are composed more readily than with the eieracnla of any of the other constituents of tho blood. Hence, these have been described under the name of the resptratory elements of the blood. The deposits of fat which are found in so many parts of the body must also bo regarded as storehouses, in which is laid up a large Btipply of fuel, or hydro- carbonaceous materials, which, in pro- cess of time, by gradually combining with oxygen, generates the proper amount of animal heal. In order to make up for the waste and destruction of these parts, which are continually ©iwyf, on, it is necessary (hat they ehottld \)6 coaB^a.'o.'A-j teifta'««i&. 106 ANIMAL HEAT. This ia eSected b^ taking as food a. proper nmoiint of fal^ t saccharine matters, or of substancea nhicL, \}j (lie act id digcEtion, can be converted into tliein. In the very cold climates of the Arctic regions, where the external aimoBphere rapidly tends to lower the temperature of the body, a large amount of fattj and oily materials forms a considerable proportioa of the food. Trayellera in those regions tell us of the enormous quantity of blubber that the Eaquimaux devour at one meal. However disagreeable this may appear to those unaccustomed to such an oity diet, yet it ia almost essential to the production and preservation of the proper amount of animal heat in those regions of excessive cold. In hot climates, on the other hand, where the demand for this excessive combus- tioD is not so great, the food of the natives does not conl^n sa large a proportion of fat. As a forcible example of the use of fat io the animal economy, the phenomena of hybernation may be adduced. There are certain animals, such bs the marmot and dormouse, which grow very fat dunng the summer and autumn. Aa winter approaches, they pass into a torpid coniiition. They live through the winter in thia stale, neither moving about, nor taking food, — the heat of their bodiea, during thia period, being maintained by the slow oxidation or combustion of the fat which had been atored up in the aystem previous to the commencement of winter. The fat being consumed by thia procesa, they are necessarily at the end of winter apare and thin, Man, above all animals, appears to have the power of living in the greatest range of temperature. This he is enabled to do, partly by the power he possesses of accommodating his food to the nature of the climate in which he is for the time residing; and partly alao by the external aids, such aa fire and clothing, which he is enabled to call to his assistance, Arctic navigators have experienced cold as low as 70° or 102° below the freezing point, whilst within the tropics the temperature Jibove 100". A very high degree ot ftvtiftcial heat cas^ THE FOOD. 107 experienced also without iDConvenience. Men engaged in cer- tain occupations, as in iron foundries and glass works, being for hours exposed to a very high temperature. The heat of the body does not in these instances rise above 100% owing to the great evaporation or perspiration taking place at the surface of the skin. Hence, a dry atmosphere, by promoting evaporation, enables a much higher temperature to be endured than a moist one. The young of man, as well as of all animals, do not possess so great a power as the adult of resisting alternations of tempera- ture. This is especially true as regards their power of resisting cold. It is thus a matter of great importance that, during cold weather, children should be warmly clothed. The same remark also applies to old persons, for in them the different vital pro- cesses are carried on slowly, so that they require assistance from various artificial aids, both warm clothing and external heat, in order to keep up the temperature. CHAPTER XL THE FOOD, In order that no evil effects may result to the body from the waste or loss that is continually taking place in it during the respiratory and the other important processes that it performs, it is necessary that a regular and constant supply of fresh material be added to it, for the purpose of renewing those parts that are worn away. The new material is furnished by the food. To man is accorded the privilege of drawing his food from a greater variety of sources than is possessed by the rest of the animal creation. Most animals possess the power of eating only one particular description of food. Thus, one great class llve^ only on matenala derived from tlie -vegeleKV^ Yvck^^wsi^ Sx^\si. 103 THE FOOD. which thej are called herbiyoroufi or graminivorous ; olhers again eat only the flesh of animala, hence thoy are caUed carnivoroua, Man, howorar, owing to hia capabilities of liring upon both descriptions of food, has been called omnivorous. lie is enabled thus widely to draw the materialB for his support, partly through the etructurc and arrangement of his digeslive orgnna, and partly through this circumstance, that, by bis intelligence, he can, by cooking, reduce substances of an ap- parenlly hard and indigestible nature to a condition in which they can be readUy absorbed, and rendered fit for the nourish- ment of the body. It is from this power of drawing his food from BO wide a range of substances, as well as of resisting great changes of temperature, that man can live in so many different In whatever country be is placed, be can always maintain life upon the description of food found there ; and further, the odible malerials naturally existing in any country are always tha best adapted for the food of those that inhabit it. KindB of Pood. — Numerous aa the substances are that we eat, and apparently diverse in their composition, yet they may be reduced to three or four great classes : — 1st. Those in which there is a preponderance of saccharine matters, or of substances that, by the process of digestion,' can be converted into sugar. 2d. Those in which oleaginous or fatty matters form the cMaf Sd. Those in which there is an excess of albuminous matters, — that is, of substances containing nitrogen as an important element in their composition. These three claases are generally described under the name of the cranio materials of food. We have already seen, however, in the chapter on the Blood, that certain salts and other inorganic matters form an essential feature in its composition. These also must be supplied by the food, in which they are found in coTtt\m>a\iW., like ihe pea and bean. leruminQ ; m tt\ifte&& m& ik&, ^\ia£vvi% 110 THE FOOD. in the white of egg, albumen ; in the flesh and blood of different kinds of aDimnls, albumen and fibrinc. This group owes its importance to this circumstance, that after it is received into the blood, it is applied to the nourisliment of the nervoua and muscular tissues — tissues which play such an essential part in the animal economy. As the albuminous group constitutes so large and important a part of the blood, the substances compos- ing it have been described under the name of tJie sanguineous or blood-making elements of nutrition ; wliilst the oleaginous and saccharine groups, being principally employed as agents in the process of respiration, have been classed together as the respirft- tarj elements of the food. Since the difierent groups thus subserve different purposes in the economy of the animal, it is necessary that the food should contain a due and proper mixture of these groups, and not bo eseiuaively confined to one of them. All judicious diet scales are foanded upon this principle ; for experience has shown that the attempt to live o 1 one of these gi-oups alone, without per- mi t ting a proper admi cture oi' the others, is sure to bo followed by disease and death. In some of the most generally employed articles of food, two or more of these groups are combiaed. Thus, bread is composed of gluten and starch ; an egg contains albumen in the white, and fatty matters in the yolk ; milk, again, contains the albuminous principle, casein, the saccharine prin- ciple, sugar, and oily matter, butter — the whole being held in solution by water, in which also are dissolved tlie inorganio salts. In milk, an article of food is provided which, by itself, is capable of supporting life. This is instanced in the young of numbers of animals, whose food for a considei'able length of time consists of milk alone. The temperature of ihe country In which a man lives, and the habits of the individual, influence the proportion in which a mixture of these diflei'ent groups should be made. Thus, in very cold ctimalea, a large oleaginous matters can be eaten with impunity, nay, a] nbsolateJ^ esaentiid to carrying on fee ca-WAn twattloii. !^ THE FOOD. Ill hot climates, on the other hand, the necessity of taking much fatty matter in the food is almost done away with altogether ; but instead there is a craving for fruit and vegetables, in which the saccharine group abounds, — this group, possessing the same function of affording respiratory elements as the oleaginous, only not to so great a degree, so that it is less heating in its nature. Where the mode of life pursued calls forth a large exercise of muscular or nervous force, then th« albuminous group must con- stitute a considerable proportion of the food, in order to repair the waste that necessarily takes place in the tissues in which those forces are manifested. Hnnger and Thirst. — ^K the system is not supplied with food at the proper time, then the sensation of hunger is experienced : this is referred to the stomach. If through any cause the supply of liquid is withheld, then thirst is experienced : this is referred to the back of the mouth. The sensations of hunger and thirst, although referred to certain localities especially, yet are expres- sions, on the part of the system, of the want of a due supply of solid and liquid nutriment. If food be entirely withheld, then starvation is produced, and the individual dies. In death by starvation, the body by degrees wears away, and becomes daily thinner and thinner. The ever-acting respiratory function gradu- ally, yet surely, burns up the combustible part of the body. All those storehouses of fat which may have been accumulated in various parts, are, step by step, consumed ; and when, finally, through their exhaustion, all the proper materials of combustion being consumed, the parts most essential to life, such as the blood, the nervous and muscular tissues, begin to be acted upon, then death rapidly takes place. The length of time that life may be supported without taking food does not appear to be more than a week. If, however, small quantities of drink be taken, even plain water, existence may be prolonged for a few days longer. OBGAMS AND FKOCEES OF DIGESTION. CHAPTEK XIL OBGAN8 AND PROCESS OF DIGESTION. 3 the materiala that ore required by the body in order its growth, or to maintam in a state of eEScienc^r those parts that are continually being worn away la the performance of its various dutica. It will now be necessary to inquire into the agents, or apparatus, by means of which these rarioua sub- stances ara reduced to a state in which they may be absorbed into the blood, and assimilated to the composition of its different parts ; for the greater part of the articles used as food are not, even though they have been in the first instance cooked, in a state in which they can be directly absorbed into the blood. Mastication. — The food Is, in the first instance, placed in the mouth. If in the fiuid Btate, it is at once swallowed ; if in the solid form, it must bo reduced to the slate of pulp. This ie effected through the instrumentality of the Teeth. Tile teeth filed in the lower jaw are raised and depressed by the action of the muscles of mastication moving that jaw, so that the food is pressed between them and the corresponding teelh in the uppw jaw, a lateral movement being at the same time communicated to the teeth in the lower jaw, so that the food is, as it were, triturated or ground between the opposing surfaces of the teeth. The tongue, lips, and large muscles of the cheek assist materially in this process of mastication, for they press upon the food, so aa to retain it between the grinding surfaces of the teeth. At the time that this is going on, a large quantity of fluid, ibo Saliva, is poured into the mouth. The saliva is formed in the large glands called parotid, placed in front of the ear, Fig, 1, 1, and suhmasillary, 2, and sublingual, /j-'n^ nnder the tongue, 3. It paaaoa tiom \,Vim6 %\e.ada throosh ORGANS AND PBOCESS OF DIGESTION. 113 the tubes or ducts, 4 and 5, which, commencing by one extremity in the substance of the gland, open by the other into the cavity of the mouth. The formation or secretion of saliva is continu- ally going on, so as to keep the interior of the mouth moist ; but during the period of mastication, the secretion of this fluid is greatly increased in quantity. The mere thought of food, especially to a hungry man, produces an increased flow of saliva, causing <^ the mouth to water." As the saliva flows into the mouth, it becomes mingled with the food, softens it, and thus materially assists the teeth in reducing it to a state of pulp. The secretions of the above-named glands are not, how- ever, the only fluids poured into the mouth ; for beneath the whole extent of the sofl, moist, mucous membrane lining this cavity, are a number of small glands, the secretion from which aids materially in reducing the food to a pultaceous mass. The teeth, which are the chief agents in the trituration of the food, vary considerably in number at different periods of life. In early infancy, they have not appeared above the gums, for at this period they are not required — the infant drawing its supply of nutriment, in the fluid form, from the milk of the mother. At about the seventh or eighth month the teeth begin to penetrate the gums ; this gradually going on to the age of three years, when the first set, or milk teeth, are completed. These teeth are twenty in number — ^ten in each jaw. Between the age of six and seven, the milk teeth begin to decay, loosen, and gradually drop out ; the permanent set of teeth at the same time appearing, and taking the place of the . temporary teeth. The eruption of the permanent teeth continues to the age of from twenty to twenty-five, when it is completed by the wisdom teeth, which are the last in projecting through the gums. When the process is completed, the permanent tfie^ are thirty-two in number — sixteen in each jaw. Fig. 2 affords a view of the permanent teeth. They have received the following names : — The four front te^tk^ a^ %2t^ called incisors; the pointed tooth ou eaO^i «^\^^ ^l 'C(i^^^ 'V>^ 114 0H6AN3 AND PBOCE83 OP DIGESTION. canine ; the next five teeth on each side, e, molars ; — last has had the special name of wisdom tooth given to it, — M that in each jaw there are four incisors, two canines, and ten molars. Of the teeth, the incisors, from their sharp, knife-lite edges, are designed for biting or cutting the food. The canines, the upper pair of which, popularly called the eye teeth, are larger than the lower, are much leas developed in man than in dogs and other carnivorous animals, in whom they are especially adapted for seizing their prey, and tearing it to pieces. The molars and wisdom teeth are the true grinders ; their broad crowns, and the irregular character of their surfaces, eminentlj fitting them for bruising and crushing the food. Each tooth is divided into three parte — the crown, the fiuig, and the neck. In Fig. 3, e represents the crown : this is the part that projects above the gums into the cavity of the mouth; /represents the fang : this la the part by means of which the tooth is fixed in the hollow or socket in the jaw. Each canine and incisor only possesses one fang, but the molars and wisdom teeth have either two or three fangs. The neck, ^, is the part where the crown and fang join. The gum closely surrounds and embraces the neck. Thecrownof the tooth is covered by a white, extremely hard substance, called the enamel, /i, which, owing to its being with difficulty acted u[)on by any of the mateiiala taken into the mouth as food, assists most efiectivelj in preserr- ing the crown from injury. The fang of the tooth is covered by a thin layer of bone-like substance, called Hoolh-bone, I'.l The great mass of the tooth is made up of the substance called dentine or ivory, t. This passes upwards into the crown, and downwards into the fang. It contains in its interior a'cavity, I — the pulp cavity. The whole of the substance of the deutino is permeated by a large number of canals, tn, which open by ono extremity into the pulp cavity, from which they extend to tba outer part of the dentine. JEach tooth has a nerve and artery passing to it, and a ti /og Svin it These enter the pulp cavity ftn»\i^ b. holft, fl k«^ m OHGANS AND PBOCESS OF DIGESTION. 115 and 3, n, in the bottom of the fang, and then run upwards to the top of the cavity. It is by exposure or irritation of the nerve in the pulp cavity of the tooth that the pain of toothache is produced. Deglutitioil. — ^The food is now in a state fit for swallowing. At the commencement of the act of swallowing — deglutition, as it is termed — ^the bolus of food is collected upon the upper surface of the tongue, 6, the tip of which is pressed against the roof of the mouth. By the contraction of the muscles of the tongue, the bolus is forced backwards through the opening at the back of the mouth into the pharynx, 7. The muscles forming the walls of the pharynx, 8, now contract, and press the bolus downwards into the esophagus or gullet, 9, the muscular fibres of which, in their turn, contract so as to force it into the stomach, 10. As the food passes through the posterior opening of the mouth, it is lubricated by the secretion formed in the tonsils, 11, one of which is situated on each side of this opening. The mouth is not the only cavity opening into the pharpix, for it coinmunicates also with the respiratory passages, both the nose and larynx. It is an object of great importance to prevent, during the act of deglutition, any portion of food passing up- wards into the nose, or downwards into the larynx or wind-pipe. A special apparatus is provided, by which this is guarded against. Every time that we swallow, the soft, pendulous palate, 12, at the back of the mouth, is raised and brought in contact with the wall of the pharynx, so as to form for the time being a complete partition between the posterior openings of the mouth and nose. Sometimes, as when laughing during the act of swallowing, the soft palate does not act properly, and then the food, especially if it be in the liquid form, returns through the nose. The upper opening of the larynx is guarded by a yalvular body, called the epiglottis, 13, which, for the most part, 18 erect, so as to allow air to pass freely fi:om the mouth into the wind-pipe in the act of respiration ; but during swallowing it IS depressed, and, as seen in the figure, courgloiX/^V^ ^q^^t^ ^^ orifice of the larynx. If througli any c\tc\xTas\»jic^ ^Os^a ^^n^ 116 OBGANS AKD FBOCEBS OF DItiESTIOIf, ■ind-^^^ should not act properlj, the food would pass into the wind-f and death by suffocation would be produced.* Action of the Stomach. — The food having thus reached the stomach, the muscular fibres iu ils walls contract, so as to move the food about from one end of the stomach to the other, causing it to perform this revolution several times. At the same time a quantity of fluid, the gastric juice, is poured out from numerous small openings in the inner surface of the stomach. By the movements of the food, this fluid becomes thoroughly miseil with it, and converts it into a semi-fluid material, called diT/me. In Fig, 4, we have a view of the interior of the stomach, the anterior wall having been removed. The whole of the inner surface is lined by a smooth mucous membrane, in which are seen the numerous small openings through which the gastric juice is poured. In Fig. 6, these openings are seen greatly magnified. Each of these openings leads into a small pit, from which several fine tubes pass. These tubes are lined by a number of very minute pai-ticles or cells, repre- sented in Fig. 6 very highly magnified, in whieh the gastric juice is formed. The walls of these tubes have ramifying upon their exterior a fine network of capillary blood-vessels, from the blood flowing along which these cells possess the power of form- ing the gastric juice. It is by the bursting of these cells, or by its transudation through their walls, that this fluid becomes dis- charged into the cavity of the stomach. The distension of the stomach by the food causes its anterior part to be raised upwards against the under surface of the diaphragm, 14. This, to some extent, interferes with the descent of this muscle during inspira- tion ; so that, after taking a full meal, active and violent exercise is always difficult to perform, for the free action of one of the most important of the inspiratory muscles is impeded. ' In the figure, the pharjai haa been forcibly drawn to one side by 1^ bonk, in older to give a view of the parts nbove ileitribcd. The rt tire re\MXoTis of these different openings with [heir protectiog Ti aeen to greater advanlage in Plato TUI.,"Ei£, \&. rhe r o i p BH I 'M ORGANS AND PROCESS OP DIGESTION. 117 The food is prevented passing out of the stomach until it is properly chymified, by the contraction of the muscular fibres at its smaller or pyloric end, Fig. 1 and 4, 15. These form a cir- cular valvular constriction around this part of the stomach, which is relaxed at intervals as the chymification of the food gradually becomes completed. Action of the Intestine. — The chyme now enters the Small Intestine, in the upper part of which, called the duodenum, 16, it becomes mixed with the bile secreted by the liver, 17, and the fluid secreted by the pancreas, 18. It is gradually propelled by the contraction of the muscular fibres in the walls of the duo- denum into the other parts of the small intestine, viz., the jejunum, 19, and ileum, 20. The mucous membrane lining the inner sur- fisice of the small intestine, presents myriads of minute orifices on its surface. These orifices lead downwards to fine tubular depres- sions, seen in Fig. 7, a a, called the glands of Lieber-ktihn, afler their discoverer. These glands are lined hy minute particles or cells, similar in shape to those lining the glands of the stomach, represented in Fig. 6. Through the action of these cells upon the blood flowing in the capillaries on the outside of each Lieber- kUhnian gland, a fluid is secreted, which is poured into the canal of the- intestine during digestion, and which becomes, by the movements of the bowels, thoroughly mixed with the chyme. Through the agency of this fluid, together with the biliary and pancreatic fluids, the chyme is converted into chi/le. As the chyle flows along the small intestine, there are separated from it all those portions which are to be employed in the nourishment of the body. The residue, or refuse portion, passes into the large intestine, 21, to be excreted from the system.^ To the canal, commencing at the mouth and terminating at the end of the large intestine, along which the food or aliment passes, the name of alimentary canal is given. The muscles moving the walls of * In the figure, a portion of the large intestine passing transversely acroBs the abdomen, so as to unite the two parts figaxed2\^^ws^"a^^ P^P 0BGAN9 AND FBOCESS OF DIGESTION. ^^^^| ^tery, also passes to tbe liver, for iLe purpoae of conveyin^^^^H blood that has lo nooriah it, for Ihe liver is not nourished by th« ' blood flowing through the portal and hepatic veins. Filling up the spaces between the capillaries of the portal veins are a very large number of minute microscopic objects, the secreting cells of the liver. In Fig. 9, they are represented highly magnified. These cells lie in close contact with the capillaries, and it is by their agency that the bile b separated from the blood. Each ciell coutaiiis in its interior minute drops of bile ; after a Ume tlie cell bursts, and discharges its contents into ihe fine com- mencement of the bile duct The numerous small bile ducts gradually converge, so as to form one large duct, s, which leaves the liver at the transverse fissure. This duct, Fig. i, s, may be seen entering the duodenum along with the pancreatic duct. As the bile is only required during the period of digestion, and as the secretion of the bile from the portal blood takes place at ' other times than the digestive period, a reservoir has to be pro- Tided to contain it until such times as it may be required. This is furnished by the Gall- Bladder, 24, which communicates by means of a small duct with the bile duct. The gall-bladder Las in its walls involuntary muscular fibres, which, when the n bile is required for digestive purposes, contract, so as to force it into the intestinal tube. The separation of the bile from the blood is not the only im- J portant function performed by the liver, for it is in this gland that the sugar is formed which plays such an important part ' in the function of respiration. For it has been found that the blood of the hepatic vein — that is, the blood leaving the liver — alnrays contains an appreciable amount of sugar. With regard to the uses of the bile in digestion, there is i considerable difficulty in forming a correct opinion. It ap- pears to possess the power of checking any tendency to ter- • mentation or putrefaction in the food as it passes s inteatinul canal. Thus, when the secretion of tbe bi proporlf going on, and there is conae4\a«,ivt\^ a deficlem le ia^^J ABSOBPTION. 123 this fluid in the intestine, certain putrefactive changes probably take place in the food, which produce some forms at least of that most Protean malady, indigestion. The presence of bile in the intestine appears to stimulate generally the functions of this canal, partly by promoting the secretion from the glands and partly also by exciting the contraction of its walls. Action of the Intestinal Secretion. — ^The amount of secre- tion produced in any single intestinal or Lieber-kiihnian gland is only small; yet, when the great length of the small intestine is considered, amounting to about twenty feet, and the close manner in which these glands are packed together along its entire extent, it must be obvious that the combined secretion of the whole must be considerable. As it is not possible to collect this fluid, its use cannot be ascertained very well by experiment ; but it has been conjectured that, along with the pancreatic fluid and saliva, it assists in rendering soluble the farinaceous part of the food. It is also probable that, together n with the pancreatic fluid, it assists in the absorption of fatty matters, by saponifying them, or converting them into an emulsion, which can be readily taken up by the absorbents. CHAPTER Xm. ABSORPTION. t ABSOBFnOK FBOH THE DIGESTIVE CANAL. As the alimentary matter can only be applied to the nourish- ment of the body aflter it has been received into the blood, it will be necessary, in the next place, to consider the mode in which it passes from the digestive canal into the blood-vessels. This may take place in two ways, — either through the agency of the capilla27 Wood- vessels, which raimS^ \ie![i^«>.^ ^^ \a;»5iwi& 124 ABSORPTION. membrnne of tbe stomach and inteBtines ; or by a special Bet of veaaela, called absorbing Yesseb, wbicb, under the name of lacCeals, arise in tbe mucous membrane of the small in- testine. Absorption by the Blood -VesBels. — Tlio capillaries lying beneath the mucous membrane of tbe elomach, Fig. 5, p, pos- sess the power of absorbing from tlie alimentary matter con- tained in the cavity certain of its constituents. Thus water, and any substances which it may hold in solution, readily and rapidly pass into the blood-vessels of tbe stomach ; so that when a draught of water is swallowed, it at once en- ters the circulation throogh iho capillaries of tlie stomach, without ever passing into the intestines. The capillaries of tbe intestines also share with those of the stomach in this power of absorbing fluids. If the intestinal mucous membrane is ex- amined, a number of fine processes may be observed projecting from it into the intestinal cavity. These processes, called villi, are represented considerably enlarged in Fig, 7, b b. In the interior of these processes the blood-vessels form a fine capillary network, c, which possesses a considerable absorptive power. In Fig, 7 only the blood-vessels in two of these processes are represented, yet they exist alike in all. The materials over which the blood-vessels especially exercise an absorptive power, are water, and those substances which it may contain in solution, such as salts, odorous and saccharine substances, together with email quantities of fatty and soluble albuminous substances. The absorption of fluids by the blood-vessels takes place most rapidly when the stomach or intestines do not contain any solid matter. Their absorption is also facilitated in those instances where the capillaries are nfttgreatly distended with blood. All the materials absorbed oy^th^loodr vessels from the alimentary canal, before passing into the stream of the general circulation, necessarily pass through the liver by the portal vein. In this oT^an those imjIortaDt changes take place which result in certain of their coDstitueQta being con\CTV&i «Ati ea^ps. .and I ABSORFIIOK. l: in the separation from them of ihoae aubslances which compoM the bile, as has abeaily been described. Abaorptioa by the Lacteals. — The elongated villous pro- cesses, Fig. 7, b b, contain, in addition to tbe capillary blood-vessels, a. fine luhe, which, under the name of lacteal, possesses the power of absorbing certain of the alimentary constituents. Each villus possesses a fine lacteal, represented at d. This lies in the centre of the villus; the blood-vea- Bels, c, on the other hand, are situated close to the wall. It is a dilficult matter to make out how tbe lacteal begins. Some physiologists have represented it, as in the figure, as formed by the junction of a number of fine rootlets ; others, however, regard it as arising by a dilated end. Each lacteal passes down to the base of the villus, and there becomes con- nected to (he lacteab proceeding from the adjacent villi, so that by their junction comparatively large vessels are formed. These leave the intestine, and pass to the back of the abdomen, within the fold of peiitoneum, which retains the intestine in its position. In Fig. 10 a small portion of intestine, e, is seen with the lacteals, d, leaving it, and passing to the back of the abdomen. There they congregate together, so as to form a large vessel, which, under the name of thoracic duct, /, extends upwards along the back of the chest, reaches the root of the neck on the lefl side, and opens into the venous system at the junction of the large jugular and subclavian veins, g. Each villus has upon its outer surface a fine lajer of cylindrical particles, Fig. 7, i. As the chyle passes along the small intestines, the process of absorption commences ; the fine particles upon the surface of the villus swell up, BO as to assume the appearance represented at Jt, owing to the passage of chyle into their interior. From these par- ticles the chyle passes into the villus, causing it to become dis- tended, and appear as if its upper extremity was filled with a num- ber of oil drops. The chyle then enters the lacteals, and through these fine tubes it is conveyed to the thoracic duct and the great reins in the neck, in the manner alreadj iescrAiti, "^^ftft ^^"^ 1 oM ^^H ro- ^^1 ary ^H 126 AB80BPTI0N. having eotered the reins, flowa along wilh the blood tc auricle of the heart, where it becomes mixed with the blood proceeding from the other parts of the body. Thus in a very short time it becomes difiiieed ihroughout tbe whole circulatory fluid. The length of tube along which the chyle has to go, from leaving the intestine to entering the blood, enables certain im- portant changes to take place in it, which adapt it in its con- stitutiun to that of the blood, and render it more iitted to be raised with that Important SuH. One of the moat remarkable of these changes is the appearnnce in the chyle of a number of small corpuscles, similar to the white corpuscles of the blood. The chyle has a, white, milky appearance ; and as it enters the lacteals, the estreme transparency of their walls allows thia milky colour to be seen through thera, from which circumstance they have received the name of lacteal vessels. The lacteala share with the blood-vessels in the power of absorbing the albuminous and saccharine parts of the food ; but in addition they also possess the power of absorbing the fatty constituents, the fat having been previously reduced to a state of the moat minute division through the agency of the pancreatic and intestinal secretions. The presence of these extremely minute fatly particles coromuuicatea to the chyle its milky appearance. pVlAod- ABSOBPTION Br TDE BODY GENEKAIXT. power of absorption ia not exclusively confined to the essela and lacteals of the digestive canal. All the soft tissues of the body that are permeable to fiuids, appear, to aome extent at least, to possess this power. Amongst these may be named the skin. Lying immediately beneath the skin, in the different parts of the body, are a num- ber of fine veasela, which are called lymph vessels, or lymphatiee. ^^^^)bese are represented ia Fig. 10, II. They are very aq^^^J ^^^Htf SJV not readily Been, unlesa the^ \kQ,^e be«,n Qrevi^^^^| ABSOBPTION. 127 filled with mercQiy, when they assume the beaded appearance represented in the figure. In their course, thej extend upwards to the trunk, and on their way they always pass through one or more bodies called lymphatic glands, fn^fn^nn. They are most abundant beneath the skin, but a few lie deeper, accompanying the chief artery of the limb, as seen in the left arm and leg of the figure. These also pass upwards to the trunk, and through one or more lymphatic glands. Having entered the trunk, the great majority join the thoracic duct,;/!. The fluid they con- tain is thus mixed with the chyle from the lacteals, and with it enters the venous system at g. Those that do not join the thoracic duct, open, by means of a distinct duct, into the veins on the right side of the neck at -n. . <^ There are numerous fnstances recorded which show that the skin does possess the power of absorbing fluids. , Thus, if the whole body be immersed for a time in a bath of warm water, it is found to undergo an increase in weight, even although, during this period, a considerable evaporation of watery vapour has been taking place from the surface of the lungs. And experi- ence has shown, in the case of shipwrecked sailors, that immer- sion of the body, or only a part of it, in sea water, has checked, £oT a considerable time, the torments of thirst. This is to be accounted for, partly by the absorption of the skin, and partly by the hinderance which the immersion necessarily places upon the evaporation which would otherwise take place from the surface of the skin. The absorption is effected, partly by the lymph vessels above described, and partly by the capillary blood- vessels^ with which, as we shall afterwards see, the skin is most^ abundantly supplied. The function of the lymph vessels does not appear, however, to be confined to the mere process of absorption from the surface. For this, it must be remembered, is not constantly going on, but is only required in certain exceptional instances. These vessels are really for the purpose of assisting in c»ll3M^ During liie last two or three jeara, the inquiries of gerBral tt tomists have thrown a new light upon this question. Fig. 4 is a diagram which wiU illustrate the iileathat baa been arrived at by these researches into the structure of the cord and the mode of terminntioii of the nerves in it. It consists of a vertical section through the cord from the anterior, k, to the posterior, t, nerve roots on one side. It will there be seen that, when the anterior cerve roots enter the cord, they connect them- selves immediately to the nerve cellR, i, situated in that part of the cord which they enter. In the diagram only one fibre of each anterior root and only one nerve cell are represented for the sate of simplicity, but all the fibres of this root must be regarded as joining nerve cells in a similar manner. The libres of the posterior root, i, on the other band, appear to consist of two distinct sets, of which one, immediately after entering the cord, ascends, I, and passing upwards through the medulla, most probably becomes connected with the grey matter in one or other of the divisions of the brain. The other, how- ever, passes considerably forwards, m, and joins the nei-ve cell to which a fibre of the corresponding anterior root has proceeded ; at least, such is the most simple way of viewing it. But there are reasons for supposing that, instead of at once joining this cell, it is connected to a nerve cell at its own aide of the cord, which, through its elongated processes, is closely connected to the motor nerve cell. For, although only one cell Las been figured, yet the grey matter in the interior of the cord, and consequently the nerve cells, are ia considerable abundance. Thus the nerve roots on the same side of the cord are brought into commuiiica- tiou through the agency of the nerve cells. In a similar manner the nerve cells on opposite sides of the cord communicate, so that the nerves constituting each pair are, to a certain extent, brought into relation with each other. The diagram also represents a long filament, n, extending upwards from the anterior nerve cell. This ascends through the anterior part of the medulla, and con- necCa the anterior nerve cell witli tlbe ViTam. 'tViia eaali aerve CEREBRO-SPINAL NERVOUS AXIS. 141 root is to be regarded as in communication with the brain, through the agency of the spinal cord and medulla : the posterior root directly through the filament thaf passes from the root directly upwards ; the anterior root not directly, but through a filament proceeding from the nerve cell with which it is continuous. These various longitudinal filaments are clustered together in different parts of the cord ; those belonging to the posterior root being situated in the posterior part of each lateral half, constitut- ing what is called the posterior column ; and those belonging to the anterior root, in the anterior part of the same half, forming the anterior column. The spinal cord is thus seen to be made up of numbers of nerve fibres and nerve cells. The great majority of the fibres extend in the longitudinal direction, and are for the purpose of connecting, either directly or indirectly, the nerve roots with the brain. The nerve cells connect the difierent nerve roots to each other. The spinal cord is consequently both a conductor and originator of nerve force. Before considering its function, however, it may be as well to say a few words respecting the distribution of the numerous nerves proceeding from it. Spinal Nerves. — These nerves almost correspond in number to the vertebrae, between which they pass in their course outwards. They present, in difierent parts of the trunk, difierent arrange- ments ; the most simple, and consequently the typical form, being seen in their course in the region of the chest, 4. Here each nerve passes directly outwards in the space between the ribs as far forwards as the breast-bone, becoming gradually smaller in its course, for it sends ofi* filaments in its passage to the muscles occupying the intercostal space and the skin over it. In the regions of the neck and loins, however, the nerves are arranged in a more complex manner ; for it is from these parts that the nervjes going to the extremities proceed. Instead of pursuing a straight course, the nerves, in these different regions, come to- gethet) so that their fibres are intermingled one with th& q^^<^x. These are called plexuses. From the tYJfo ipV^^xxa^'^ Va. ^^ w^^-* 1 42 CEEEBEO-SPINAL NEHV0U3 AXIS. 5 and C, the nerves proceed which pa«s to the arm. These more especially from the lower one, 6, which is mucU latter thHti the upper. It is caUeJ the hrachial plexus. The nei'ves which arise from the lower pari of the spinal cord also form two large plexuses, 7 and 8, from which the nerves that pass to the legs pro- ceed. By the intermingling of the nerre fibres whidi takes place in these plexuses, the branches proceeding fiwrn ihera are brought into connection with a greater extent of tlic cord than they would have been if no such intermingling had taken place. The various large nerves going to the arm, pass some on the outer side, others on the inner, others in front, and others behind. In their course they give off numerous branches, of which some enter the muscles, ami others pass to the skin. Some of the nerves are continued down as i'ar as the tips of the lingers ; these are called the digital nerves, 9. The upper of the two plexuses, from which tlie nerves of the leg proceed, sends oiF those branches which pass to the thigh, more especially the large nerve, called anterior nerve of the thigh, 10, which gives off numbers of branches both to the muscles and akin, From it also a large branch, 11, proceeds, which is distributed to a part of the skin of the leg. The lower one supplies the hack of the thigh and the remaining part of the leg and foot, especially through the large nerve, which, under the name of sciatic, 12, extends down the hack of the thigh. It divides just above the ham into two large branches, which supply the muscles and the greater part of the skin of the leg. Some of these branches may be traced down- wards as far as the toes, along the sides of which, under the name of digital nerves, 13, they extend. In the loft leg of Fig. 1 a view is given of the various struc- tures that enter into the composition of a limb. 14 represents the muscles attached to the bones for the purpose of moving them. These are retained in their position by the strong fasciOf 15. Lying beneath the fascials the large artery, 16, which con- veys the blood for the purpose of nourishing the diiferent tures. The greater part of this \csse\ caTv\;TO\)i«a ^as»CL oJl \ift»x>s^%» Blj by which auditory impressions ate coiidu^\.^^« 148 CEKEBRO-SPINAL NEKVOUa AXB. The Brain. — This is tbe largest and most important c nerve centres. It occupies the large cavitj of the cranium or skull. It is divided into several portions: the Cerebrum or great brain, 32 ; the Cerebellum or little brain, 33 j and the Fona or bridge, 34. The medulla oblongata, from being situated in the cranial cavity, is often considered as one of ils divisions, but that we have already described with the spinal cord. Tbe cerebrum, or brain proper, is divided into two lateral halves or hemispheres by the iissure, 35 ; the hemisphere on one side being an exact repetition of the opposite one. So that the cerebrum is to bo regarded as a double organ, possessiag exactly corresponding parts on the two sides. Each hemisphere is subdivided into three lobes : anterior lobe, 36 ; middle lobe, 37 ; posterior lobe, 38. Each hemisphere is composed partly of grey matter or nerve cells, and partly of while matter or nerve fibres. The grey matter is in large quantity, the principal collection of it being upon the surface ; the whole of the exterior of the hemispheres having a peculiar appearance from the manner in which the grey matter is arranged. Thus it will be seen to present a tortuous and convoluted arrangement, whence the name of convolutions of the brain has been given to it. These convolu- liona are separated from each other by depressions, which extend for varying distances into the substance of the brain. The con- voluted arrangement evidently affords a much greater extent of this kind of nerve tissue, than if the surface had been quite smooth and uniform. A comparative examination of the brains of different animals shows, that the more highly organized a brain is, the more convoluted is its exterior ; for, as we ascend in the scale, the convolutions become more and more numerous, and occupy a larger surface. Thus, the brnin of man, who possesses the greatest intelligence, is the most convoluted. The deposits of grey matter are not, however, confined to the surface of tbe brain, for there are several distinct collections in the jjiteiior. The.se are situated at the base or lower surface of the cerebrum. Different names ha've^ieen givc(\\ofti'6m,\ivA\JM;^ CEBEBRO-SPINAL NERVOUS AXIS. 149 may be classed together as the great Sensorj Ganglia at the base of the brain. Connecting these different collections of nerve cells with each other are numbers of fine white fibres. Some of these unite the different deposits on the same side, so that the ganglia at the base are connected together, and each of these is again connected to the great deposit of grey matter on the con- voluted surface. Not merely, however, are the collections of nerve cells in one hemisphere connected together ; but, through similar white fibres, they are also intimately united with the corresponding deposits in the opposite. These connecting white fibres are called the commissures of the brain. Through their agency the nerve force is conveyed from one nerve centre to the other ; and by them the two hemispheres are so intimately con- nected together, that their consentaneous action is insured. In addition, numerous fibres can be traced passing upwards from the spinal cord and medulla, through the pons, to the different nerve centres in the cerebrum. Along these the nerve force, which has been transmitted to the cord and medulla by their nerves, are conducted to the brain ; and along these also the manifestations of the will are transmitted down the medulla and cord, to pass by {Le motor nerves to the muscles. The cerebellum, like the cerebrum, is divided into two hemi- spheres by a fissure. Each hemisphere consists both of grey and white matter. The surface is composed of grey matter, which is not convoluted, but arranged in a laminar manner, like the leaves of a book. Deposits of grey matter are also found in its interior. The white fibres of the cerebellum connect the different deposits of nerve cells with each other. The two hemispheres are also connected by numerous white fibres which pass across the pons. This body lies like a bridge between these hemi- spheres, whence its name. The cerebellum is also connected by white fibres above with the cerebrum, and below with the medulla and spinal cord. The pons consists both of grey and white matter ; the white matter being on the surface. It ia pimdi^«2^"^ ^iwiK^Oi'sfc^ ^*v *^^ 150 CEREBno-spnrAL nebtotts axis. white fibres cutending upwards from the medulla to the nnii of llio white fibres connecting the two hemispheree of tlw cerebellum. Cranial Nerves. — The cerebnim &nd the pons haye several large and imporlant nerves connected to them. There are Done, however, attached to the cerebellum. Thoae springing from the cei'ehrura and pons are connected to their under surface or base, and their fibres may he traced into their interior for a short dis- tance, when they are found to be connected to some of the deposits of nerve cells or ganglia at the hase of the brain. Of these nerves, some are conductors of the nerve force which induces special sensations, as llio nerve of smell, i3d| and the nerve of sight, 40. Connected also to the side of the pons is the nerve of hearing, 31 ; but this may be traced backwards to its origin in the nerve cells of the medulla. There are three amaU nerves, 41, also on each side, which regulate the movements (^ the eye-ball. The consideration of the functions of these nerves falls properly under that of the senses to which they belong, so thai shall leave them for a time. At present we shall confine selves to the nerves which pass to the face. Two large nerves on each side go to the face. Of these 42, is for the purpose of being distributed solely to the muscles, filaments entering each of the small muBcles of this region. It IS, consequently, a motor nerve. Tiirough it the nerve force is conveyed to this region, so as to put in action one or more of these small muscles. The other nerve, 43, Las a different dis- tribution altogether, and consequently a difiercnt function ; for it passes to the skin, and is thus a sensory nerve. It divides into branches before arriving at the face, so that it reaches it m three distinct localities, 43, Fig. 5. Numerous branches then pass to the diflerent parts of the skin. This nerve is not mereljf distributed to the skin ; but it also supplies immerous filaments to the raucous membrane lining the mouth and surface of the toDgae, noae, and fi'ont of the eye-baW. T^Ttm^U l.heae filameale I CEBEBRO-SPINAL NEBYOUS AXIS. 151 all sensory impressions made on these parts are conveyed to the brain. Some time before reaching the face, this nerve gives ceiiain filaments to the muscles of mastication. These di£fer from the other parts of the nerve in this respect, that they are motor and not sensory filaments ; for through them the nerve force, which sets in action those muscles, is conducted. These motor filaments arise by a different root from that which gives origin to the sensory filaments. The sensory filaments exclusively make up the great mass of the nerve. Those portions of it^ however, which contain motor filaments also, constitute a com- pound nerve. It is described by anatomists under the name of the fifth nerve. The brain and spinal cord, as they lie in their bony chambers, are not placed in direct- contact with the bone, but are separated &om it by certain membranes. Of these the one Jying next the bone is the strongest. It lines continuously the whole extent of the cerebro-spinal cavity. It may be seen at 49, Fig. 6. Closely investing the exterior of the brain and spinal cord, is a thin membrane, in which the blood-vessels ramify before they enter the interior of these organs. Covering this vascular membrane and lining the inner .surface of the strong membrane, 49, is an extremely delicate serous membrane. These membranes protect the highly delicate nervous substance of which these organs are composed. A small quantity of fluid is always found in the interior of the cranial cavity and spinal canal, in close contact with the brain and cord. It is for the purpose of protecting them from vibrations or j^rs, which, in the various movements of the body, might otherwise be communicated to them. Functions of the Cerebellum. — The cerebellum is a portion of the brain, respecting the functions of which there has been, at various times, great differences of opinion amongst physiologists. The great majority, however, from a variety of considerations, deduced fironi experiments performed on it, and observations on the effects of disease upon it, are inclined to consider that this organ possesses the power of regulating iJu^ txvon^\Cl«on& q^ '^^ l.'lS CEREBKOSPTIIAL NEEVOns AXIS. muscles, or of co-ordinating them, as it has been termed.^ this 13 meant, the facultj of colling into operation the actions of different groupa of muBcIes for the performnnce of a given object. Some of the principal eriJcnce in favour of this view is derived from the fact, that in animals that are in the habit of moving rapiclly, or that require several groupa of muscles to be in action Bt the same time, this organ ia largely developed in proportion to the rest of the brain. Man, who from the multifarious duties he ia called upon to perform, and from the great precision with which moat of hia muscular movements require to he executed, certainly requires some organ to co-ordinate or regulate these movements. In him the cerebellum is largely developed in pro- portion to the size of the brain. This power ia called into oper- ation through the fibres which, on the one hand, connect ihe cerebellum to 'the cerebrum ; and, on the other, the cerebellum to the spinal cord. In confirmation of this opinion, 'numerons instances have been observed in which, owing to disease of this organ, the muscular movements have been disturbed and irregu- lar. It must be confessed, however, that over the functions of this organ considerable obscurity exists ; so that, although there are many reasons for regarding it as possessing the power of co- ordinating muscular action, yet it probably baa other functions. What these may be physiologists have not as yet been able to discover. The recent diseoverlea in the strncturo of the spinal cord, by showing the abundant communications that exist between the nerve fibres of the same root, and the fibres of different roots, through the medium of the nerve cells, would appear to indicate that the cord itself must also possess considerable influence over the co-ordination of muscular movements. Pnnctions of the Cerebrum, — The cerebrum is the most highly endowed of the various divisions of the brain. It is the oi^n of the mind, the various operations of which are manifested throD^-h it. In conaidering ft a physiology, it i8 necftsawj Vo tcBiftiBbet i Apfllfl CEREBROSPINAL NERVOUS AXIS. 153 the grey matter found in it may be separated into two great divisions ; that found at the base of the brain constituting the sensory ganglia of the base, and that found on the surface con- stituting the grey matter of the convolutions. Each of these two divisions possesses different functions. In the sensory ganglia the sensory nerves, both those of common and special sensation, terminate ; and it is in them that those sensations are excited which render the mind cognizant of external objects. To these ganglia the motor nerves also have most important connections. It is probable that through the agency of the nerve cells, by which one set of fibres is brought into connection with another, that those changes take place which result in the reflection of impressions from one nerve to another so as to produce instinc- tive and habitual movements. The convolutions of the brain possess a much higher function than the sensory ganglia, for it is through them that the higher qualities of the mind are manifested. It has already been men- tioned, that they are more numerous in man than in any other animal ; and not only so, but they are much more perfectly developed in the adult than in the child. In those also whose mental powers are of a low order, such as idiots, the size and extent of the convoluted surface of the brain are limited. These various circumstances all lead to the conclusion, that their office is of a much higher kind than that of any of the other divisions of the brain. Owing to the manner in which the con- volutions are arranged on the surface of the brain, it is obvious that the larger a brain is, the greater will be the extent of its convoluted surface ; from which circumstance the conclusion has been drawn, that those who possess large brains will be persons of great intellectual acquirements. Observation, to a certain extent, though not altogether, has confirmed this hypo- thesis; for it has been found that most of those who have acquired great influence over their fellow-men — who have been in the true sense rulers — ^have been large-headed, large-brained men. The size o£ the head does not, howevet, sl^^t-jVm^^iaXfc ^^^^^'^ 1 154 CEHEBRO-SPISAL NERVOUS AXI8. is a large brain within, for there are several circ urn stances li ma^tend to produce a large akutl witliout the brain growing it proportionate manner, In attempting to fonn, however, an esti- mate of the extent of the intellectual capabilities from the size of the head, it must be kept in mind that the skull may be large tlirough excessive growth in one direction only j so that, allhougb there may be great size, yet the head will be badly proportioned ; H. well balanced, well proportioned skull, with its cootained bruo, appearing to be conditions essential to the possession of well regulated mentii! attainments. All physiologists agree in the belief, that the iutelleciual powers are proportioned to the development of the convolutiona. The phrenological school baa, however, gone further than this. It has attempted to prove that different parts of the eonvolulions are the seats of the different faculties of the mind, and that these are manifested by an individual in proportion to the degree In which the particular convolutions, or parts of convolutions, are developed. The disciples of this school have also stuted, that the shape of the bead, in detail, is influenced by the shape of the contained brain; and, that the size and development of die difiereut parts of the convolutions, produce corresponding eleva- tions or depressions upon the outer surface of the skull ; so that, by examining the exterior of the head, an idea may be formed respecting the size of these different organs, and the extent to which the faculties of which they are the seat are developed in the individual. Other physiolt^Bls and anatomists are not, however, willing to admit all the conclusions to which the phrenologist has arrived ; neither are tlie mental philosophers prepared to coincide with him in the divisions to which he has reduced the various menial faculties. That different parts of the brain are the seats of diSerent functions is generally admitted, but it still remains a matter of doubt where these various functions are located. Again, there can be no question that the shape of the skull affords, generally, a, very good idea ot ibe aW-ee ot \.\v& wQUined brain; SYMPATHETIC NERVE. 155 but, in some parts of the skull, there are certain modifications of its structure which entirely prevent this from being ascertained. This is especially manifested in the region of the forehead along the line of the eyebrows. In most adult heads there is a con- siderable prominence along this line, and here the phrenologist has located certain of the faculties into which he divides the mind. But this prominence is not due to a corresponding projection of the brain in this region ; it is simply owing to this circum- stance, that here the two layers of bone, of which the bones of the head are composed, are separated &om each other by a con- siderable interval, the outer one being pushed forwards in order to afford room for the frontal sinus. It follows from what has been stated, that every mental act is accompanied by some change in the grey matter of the convo- lutions. These convolutions must thus be regarded as the seats of those £iculties which make up the intellect. But that prin- ciple which regulates the intellectual and moral constitution of man — that self-consciousness or higher reason which distinguishes him from the lower animals — cannot be said to have any special seat in the brain, neither are its manifestations due to the orga- nization of the brain. CHAPTER XVn. SYMPATHETIC NEBVB. In addition to the nerves that have now been described, we have to consider a system of nerves which, under the name of sym- pathetic nerve, plays an important part in regulating the func- tions of the economy. This nerve can scarcely be regarded as belonging to the cerebro-spinal nervous system; for although many connecting filaments pass between the two, yet it possesses so many independent centres of its own, t\iaV.\\.ifiL\x«X\^^x^^S^^<^^ ^^^R^G 8TMFATHETIC KESVE. ^^^H H as, to a great extent, n separate system. The complete cOiMM^I of this nerve may be seen in Fig. 1, 44. It is placed at the side ' of the spinal column, running almost parallel to it. It extends from the first vertebra in the neuk downwards as far as the coccyx, in front of which bone the sympathetic nerve on one side joins the one from the opposite. At various points in its course, swellings or dilatations are found, which are caused by the presence of nerve cells in these localities. Each of these swellings is consequently a nerve centre or ganglion. The num- ber of these dilatations nearly corresponds with that of the vertebric. From these ganglia 51ament9 (45) pass, which connect the sympathetic to each of the different spinal nerves, se they pass outwards through the foramina between the Tertebrc. From these ganglia branches also proceed, which are distributed to the various large viscera in the cavities of the chest and abdomen. In Fig. 5 many of these branches are representedr especially those going to the heart, 4C, lungs, 47, and stomaiAf 4S. Before the branches pass to those different organs, they inter- lace so as to form large plesuses, in which interlacement ths filaments of the vagus going to the same organs also join. Fropi these plexuses, as froai a centre, numerous branches pass to Uis above named viscera. In Fig. 5, 48 represents the large plexus, from which branches proceed to the stomach and other important viscera of the abdomen. Tn conformity with the statement that has already been made, that the part to which a nerve is distributed influences munly the function of that nerve, we must suppose that the sympathetic nerve regulates the secretions and movements of the various important organs to which it proceeds. Some of these, how- ever, such as the heart, lungs, and stomach, receiving also fila- ments from the vagus, are not exclusively under its influence. tThe salivary glands also receire nerves both from the sym- (pathetic and cerebro- spinal systems. Those organs which receive their nervous supply from both systems, appear to be brought more under the influence o^ VW imtvi (.ban, those lo SYMPATHETIC NEBVE. 157 which only sympathetic filaments are distributed. This is especially manifested in the cases of the heart and the stomach ; the movements of the former organ being very much influenced by the different states of the mind. Thus, excessive fear may so £ar disturb its actions as to diminish considerably the force and number gf its contractions ; and several well authenticated cases are on record, in which, under the influence of this emotion, its movements have been entirely suspended. Similar disturbing influences are also exercised upon it by the other passions and emotions. The secretion of the gastric juice appears also to be consider- ably under the influence of the mind. Thus, it is well known, that one of the best aids to digestion is a happy and contented state of mind ; for here no disturbing influence interferes with the proper secretion of the gastric fluid. But under powerful mental emotions its secretion may be entirely suspended, so as completely to put a stop, for a time, to the digestive process. Hence the loss of appetite that almost invariably accompanies greatly excited conditions of the mind. There are a class of sensations and actions which, under the name of sympathies, were at one time supposed to be under the governance of this nerve, from which circumstance the name of sympathetic was given to it. These are supposed now, how- ever, to be under the guidance of the cerebro- spinal system ; to these may be referred pain or disturbance of function in an organ, when another organ is not in a proper state of health. A forcible example of this is presented in those cases in which palpitations of the heart are brought on in certain forms of indigestion, owing to the stomach being out of order, and not performing its func- tions properly. 1 58 ON SENSATION. CHAPTER XVm. ON SENSATION. We will now proceed to the consideration of those organs, bj the agency of which, and the nerves proceeding from them, sen- sory impressions or sensations are communicated to the mind. These are amongst the most important organs in the body, for it is through their agency that the mind is made acquainted with the various objects surrounding it in the external world. Thus, by the sense of touch, it is enabled to perceive the density of bodies, their comparative hardness, or their temperature. By the sense of sight, it perceives their size, form, and colour. By the sense of hearing, it distinguishes the various vibratory impres- sions each is capable of producing. By the sense of taste, it dis- tinguishes whether they are tasteless, that is, incapable of excit- ing the nerve of taste, or whether they cause it to convey an impression which produces in the nerve centre a sense of sweet- ness or acidity. By the sense of smell their odour is ascertained, either agreeable or disagreeable. Each of these different senses has a special organ and a spe- cial nerve for the excitation of its particular sensation ; the shape and arrangement of the organ being especially adapted for the particular sensation to which it is subservient. An impor- tant point to be kept in mind is this, that it is not in the organs of sense, as they are called, that these special sensations are per- ceived ; it is in the brain alone that this perception takes place. Each sense organ has thus its special nerve, which conveys to the brain the sensation of which that organ is the agent. Thus, from the papillae of the skin, the nerves of common sensation or of touch proceed ; from the eye the nerve of sight passes ; from the ear the nerve of hearing; from the tongue the nerve of taste; from the nose the nerve o{ &m^\V. ON SENSATION. 159 ^ Each of these nerves terminates in the brain in a distinct locality, so that it may very reasonably be inferred that the seat of any particular sensation is at the point of termination of the nerve proceeding from the organ in which that sensa- tion is excited. As these nerves all coAvey impressions to the brain, they are consequently all centripetal nerves. Although a different sensation is excited by each nerve, yet they all possess exactly the same structure ; so that we have in this a confirmation of the statement already made, that the function of a nerve is determined by the organs to which it is connected at its extremities. Every sense organ, with the nerves proceeding from it, is alone capable of exciting its own sensation — those peculiar stimuli which possess the power of exciting any particular sen- sation only acting through the organ which is set apart for the induction of that sensation. Thus we can only see with the eyes, we cannot hear or smell with them. The skin alone is eapable of inducing tactile impressions ; it possesses no power of taste. Whatever be the stimulus applied to the nerve of sight, either from its own proper stimulus, viz., the rays of light, or from an electric shock, only sensations of light are perceived by the mind. In a similar manner, whatever be the stimulus that excites the nerve of hearing, only sensations of sound are perceived. And in like manner with the other senses. Each sense organ, being thus confined to its own particular sense, is of course much more perfectly adapted for the production of that sense, than if other sensations had been combined with it. There are certain parts of the body to which nerves are not distributed at all, or only very sparingly. Hence these struc- tures do not possess any sensibility, or only a small amount. The most important of these structures are the bones, ligaments, and tendons. It has been found that all parts highly endowed with sensi- nbility also possess a lai^e supply of capillary bloodrN^%"ss\^\ •^'^^ presence oF a constantly moving and cYian^tv^ ^xatccX ^^^^ 160 THE SKIN AND COMMON SENSATION. being apparentlj necessary to the proper excitation of sen- sations. CHAPTER XIX. THE SKIN AND COMMON SENSATION. The faculty of determining the properties of bodies by the touch resides in the skin. As certain special structures are found in it for the excitation of this sense, it will be necessary, in the first instance, to consider their anatomy. As the skin, however, is not merely the touch organ, but, from its containing certain accessory structures, possesses also other properties and uses, it will be advisable in this place to consider the various structures by which these are performed. Structure of the Skin. — The best way of obtaining an accu- rate idea of the structure of the skin is to make a section through it perpendicular to the surface, and to examine this section by the aid of the microscope. Fig. 7 is a view of this kind. The skin is now found to be divided into two parts, of which the deeper is called the cutis, dermis, or true skin, o; the super- ficial being termed the cuticle, epidermis, or scarf skin, p. The boundary line between the two is well defined. Of these the cutis is the most important. The surface of the cutis, next the cuticle, is always firmer and more condensed than the deeper parts of the cutis*. In the for- mer situation it is elevated into a number of small projections, called papillae, ^, which fit into corresponding depressions in the deep surface of the cuticle. By its deep surface the cutis becomes gradually blended with the cellular tissue and fat, which forms a constant layer beneath the skin. Passing upwards into the papillae are the fine capillary blood-vessels, r, from which the blood Howa when the skin is cut ox piidL^^. l^ii^ ^^sXAii^^^iiiAo the THE SKIN AND COMMON SENSATION. 161 papillas are the small nerves of the skin, which join there a pecu- liar body, called the touch organ, s, from its supposed use in exciting the sensibility to tactile impressions. These papillae are most abundant in those parts of the body which are most sen- sible to touch, such as the palms of the hands, tips of the fingers, and margins of the lips. A surface view of these papillary projections is afforded at q, Fig. 8, from which the cuticle has been removed. The cuticle consists of a comparatively hard and dense struc- ture lying in close contact with the cutis, and not capable of being separated from it in the healthy and living skin. It is destitute both of blood-vessels and nerves ; hence it is utterly devoid of sensibility. It consists of several layers, one being placed over the other. These layers present different appear- ances in the deep and superficial parts of the cuticle. Each layer is composed of small cellular bodies called epithelium cells, which, in the deeper layers, are globular in shape ; but as they are traced to the surface they become more and more flattened, and, at the same time, harder and more horny. These changes are represented in the detached cells at the side of Fig. 7. In the deeper layers of the cuticle the colouring matter of the skin, or pigment, is found. This is much more abundant in the cuticle of the dark rsyces than in that of the fair races of man. The difference between the colour of different skins thus simply de- pends upon a greater or less amount of deposition of pigment in the deeper layers of the cuticle. Those dark spots, so fre- quently seen on different parts of the skin, called freckles and moles, are simply owing to increased formation of pigment in those particular localities. The outer surface of the cuticle, in many parts of the body, especially on the palm of the hand, is marked by ridges and furrows, presenting varying courses and directions. The ridges indicate the position of the papillse, which, by their projec- tion, push forward the cuticle covering them. The C\3x\is^\si ^ 170 THE TONGUE AND THE SENSE OF TABTE. number of projections, called the PapillaB of the tongue, which present different shapes in different parts of the tongue. Situated quite at the back of this surface are several large papillae, which, from possessing a depression around their bases, are called the Cir- cumvallate papillae, Fig. 7, g* Scattered over this surface, though most abundant at the sides and tip, are the Fui^form papillae, h. The great majority, however, of these elevations, which occupj the intervals between the two last named papillae, are called the Filiform papillae, t. The whole of these papillae are covered bj an epithelium, which, though dififering in shape from that in- vesting the papillae of the skin, yet possesses a similar function, viz., that of protection. When the epithelium collects in considerable quantity upon the surface, it produces the white appearance to which the name of furred tongue has been given. Passing to the tongue on each side is a large artery, which conveys blood to it for the purpose of nourishing it. Proceeding from the tongue also are corresponding veins, which convey away the blood after it has fulfilled this office. Fine capillary vessels are found in the papillae, their arrangement being closely similar to that figured and described in the papillae of the cutis. Three large nerves pass to each side of the tongue. Of these, one is distributed to the muscles, 29 ; it is consequently a motor nerve. The other two pass to the papillae ; these are sensory nerves. They proceed to different parts of the tongue; one to the front and sides, called the lingual nerve, 43 ; the other to the back of the organ, 30. There is considerable difference of opinion amongst physiologists as to the exact office of these two nerves. Some suppose that the lingual nerve is not the medium for ex- citing gustative sensations, but is simply the nerve of touch or common sensation. They regard the nerve that passes to the back of the organ as the only nerve of taste. Other physiolo- gists, however, are inclined to the belief that both nerves may be endowed with the power of conducting taste impressions. In the papillae, the ^laments of these netveA Xe;nxaTk^\.^\Ti'^^^\i^\^x ^^acs&sr THS EYE-BALL AND THE SENSE OF SIGHT. 171 tures, called taste organs, closely corresponding to the touch organs in the skin. It is bj the contact of sapid materials with these organs that the sense of taste is excited. In order to excite the sense of taste, it is necessBiy that the substances applied to the tongue be either in solution or capable of being dissolved bj the fluids of the mouth. For, without this, they cannot penetrate through the epithelium covering the papillse, so as to come in contact with the taste organ. The sensibility appears to be most acute at the tip, sides, and back of the tongue. The sense of taste enables us to discrimi- nate between sour or sweety and bitter or saline, substances. Great numbers of sapid materials possess a considerable odour, as in most aromatic substances. These excite the sense of smell at the same time that they influence the sense of taste, and, by the combined action of these two senses, our appreciation of the flarour of these substances is greatly heightened. The sense of taste may remain in the mouth for some time aflter the mate- rial that induced it has been swallowed. This is owing to the Bolution of the substance in the fluids of the mouth, which, by collecting about the papillae, keeps up the particular flavour that has been induced » Experience teaches us that the acuteness of this sense may be considerably diminished by taking some highly aromatic substance; for this will obscure, for a time, almost completely the more delicate flavour of any substance which may be swallowed shortly afler. CHAPTER XXn. THE EYE-BALL AKD THE SENSE OF SIGHT. The Eye-ball is the complex special apparatus provided for the reception of the rays of light, previous to the impressions pro- duced by them being conducted to the braiti« Connected with the eye'-ball are ^ettaVii CL'^^^siAA'r] %^x^^^^!Qi^^'^^ ] 72 THE EYE-BALL AND THE SENSE OF SIGHT. some of which afford it protection, others being for the parpose of moving it in various directions. These will be considered in the first instance. Acceseoty Stractnres of the Eye-Ball. — The eye-ball is lodged in a Inrgo cavity on the side of the face, external to the nose, called the orbit. The upper and lower margins of this cavity are well marlted and strong projections. Extending along the line of the upper margin is a thick fold of the skin, containing a considerable quantity of fat. This is the Eye-brow, Fig. 1, 1. The outer surface of this is closely set with short strong hura. Certain small muselea are connected to the deep surface of the eye-brow for the purpose either of elevating or contracting it. By its movements, under the action of these muscles, great ex- pression can be given to the features — elevation of the eye-brow taking place during surprise or astonishment ; contraction occur- ring during displeasure, as in the act of frowning. The eye-ball is protected by two moveable shields, called the Eye-lids, 2 ; one being in relation more especially to the upper surface of the front of the eye-ball, the other to the lower sur- face. Of the two, the upper eye-lid is most moveable. The elevation of this lid takes place through the contraction of a small muscle placed within the orbit, which, from this circumstance, is called the elevator of the upper eye-lid, Fig. 2, 3. The closure of the lids is produced by the orbicular muscle, represented in the muscular iigure at 2. Each lid is strengthened by a thin layer of cartilage contained in its interior. Fringing the mar- gins of the lids are the short hairs called Eye-lashes. Those connected to the upper lid are longer than those connected to the lower. They project also downwards and forwards, so as to overlap a considerable part of the front of the eye-ball, and thus very materially to protect it. Lining the inner surface of each lid is a smooth, moist membrane, called the Conjunctiva, which is prolonged over the front of the eye-ball. Lying on the inner surface of the lid, and covered by the conjunctiva, are a number of Bmall glaadalar bodies, called tto Me.ftwTO\Mv ^ixila., -wWiatL THE EYE-BALL AND THE SENSE OF SIGHT. 173 secrete that peculiar waxy matter which collects in greater or less abundance at the roots of the eye-lashes. The eye-lids, with their depending lashes, are most effectual means for protecting the delicate anterior surface of the eye, for, when particles of dust approach it, they at once close, almost involuntarily. They shut also when the eye is exposed to a strong and injurious light. They are kept constantly closed during sleep ; partly for the purpose of shutting off the rays of light, and partly also in order that the eye may be protected during this period of unconsciousness. As it is necessary that the front of the eye-ball should be kept constantly moist, a special secretion is provided for this purpose. This secretion constitutes the Tears. The gland in which the tears are formed, called the Lachrymal Gland, 4, is placed at the upper and outer part of the orbit.^ From it a number of small ducts proceed, which open on the inner surface of the upper lid. Through these ducts the tears are continually flowing ; in ordi- nary states, in small quantities only. By the oft repeated winking movement of the upper eye-lid, the tears are conveyed across the front of the eye-ball so as to moisten it. Certain special chan- nels are provided for carrying away this secretion after it has fulfilled its purpose. If the inner extremity of each eye-lid be examined, a small aperture, 5^ of sufficient size, however, to admit a fine hair, may be seen. This aperture leads into a fine tube or duct, the tear duct ; one proceeding from each lid. The two ducts gradually converge, join and open into a pouch-like dilatation, called the tear sac, 7. This is lodged in a depression in the inner wall of the orbit. From it a duct, 8, proceeds, which opens into the nose. The tears, after moistening the eye, collect in the groove be- tween the margin of the lid and the front of the ball. By this groove they are conducted to the small openings in the lid. ^ A portion of the eye-brow and upper margm of the otb\& Vilv^^ V^st^ been cut air ay in order to afford a view of the lac^Yiiyai^X \^\\.^« 174 THE EYE-BALL AND THE SENSE OF SIGHT. They enter these openings and then proceed along the tear duct into the sac, and so into the nose. When the tears are formed in large quantities, as in the act of crying, the small orifices are not of sufficient size to carry off the secretion. In these casea^ it runs over the margin of the lower lid and down the cheeks. Lying within the cavity of the orbit are several small moacles, which are connected to the outer coat of the eye-ball. They are for the purpose of moving it. Four of these muscles are called the straight muscles. They all arise from the back of the orbit One is inserted into the outer side of the ball, 9 ; this moves the eye outwards. Another into the inner side, 10; this moves the eye inwards. A third is inserted into the upper surface^ 11 ; this elevates the eye-ball. The fourth one into the lower sur- face, 12 ; this depresses it. By observing the movements of the eye-ball, it will be seen that, when the inner straight muscle of one eye, say the rights contracts, that eye is drawn inwards, but, at the same time, the outer straight muscle of the left eye coQ- tracts, so as to draw it outwards. The two inner or the two outer straight muscles of the two eyes cannot be made to act at the same time, except by a very strong effort of the will. When they do so, however, an artificial squint is produced. Two other muscles lying in the orbit are also connected to the ball ; these are called the oblique muscles, 13, 14. The deter- mination of the action of these muscles is an act of considerable difficulty. Their most probable function, however, is to rotate the eye-ball in the antero-posterior direction around the axis of vision, so as to bring both eyes, at the same time, into co-ordi- nation, upon a single object. The movement of the various muscles of the eye-ball is regu- lated by the small nerves, Plate VII., 41. The movements of the eye-ball are facilitated by the presence of a considerable quantity of fat in the orbit, which, acting as a soft, flexible cushion, enables the eye to move readily from side to side. Xbe Eye-BalL — The eye is Gompo^«^ o^ ^^^^t^ ^\%\.v;ict coats THE EYE-BALL AXD THE SENSE OF SIGHT. 175 or coverings, which are for the purpose of protecting the delicate nervous structures contained in its interior. In addition, it also possesses some highly delicate lenticular or refracting structures, which modify considerably the direction of the rajs of light as they pass to the retina. The eye is irregularly spheroidal in shape, from which circum- stance it has been called the eye-ball or globe. If viewed in section, as in Figure 3, it presents segments of two spheres, of which the anterior one is smaller and more pro- minent than the posterior. The convexity of these spheres is regulated by the outer covering of the eye, which consists of two structures, presenting very strong contrasts to each other in their appearance. The more posterior, called the Sclerotic coat, 15, is thick, opaque, and white. It constitutes, in fact, the white of the eye. It is not confined in its position, however, to that part of the eye-ball which can be seen between the lids, but it extends backwards so as to invest the entire posterior surface of the globe. It is com- posed of fibrous tissue. By its great strength and inelasticity, it protects most effectually the back of the globe,'and gives to it a permanent shape ; the latter being a very essential quality, when it is remembered, how necessary it is, that the delicate internal lenticular organs should preserve their proper form. The more anterior part of the external coat is the Cornea, 16. It constitutes the beautiful transparent structure at the front of the ball, through which all the rays of light proceed in their pas- sage backwards to the retina. It is firmly connected by its circumference to the sclerotic. Although perfectly transparent, it yet possesses considerable strength and thickness. It is thus capable of effectually preserving the proper convexity of its light- transmitting surface. Immediately within the sclerotic, lying next to it, and extend- ing almost as far forwards, is the Choroid Coat, 17. This coat is comparatively thin and delicate. It is of a deep black colour. It Owes its colour to the "^Yea^xic^ ol ^\ax^ ojsiaKi.- 17G THE ETE-BALt AND THE SENSE OP StG'S^. tit^ of pigment. Id addition, it contains a number o veaseb, both arteries and veins, which enter the eye-ball at the posterior part. They pass through tbe sclerotic coat and run forwards in the choroid for the purpose of conveying blood t o fee different structures. The cboroid t«rroioates in front in a number of ling cesses, called tlie Ciliary Processes, 18. ConDocted to the outer surface of these processes are a number of fine fibres which are undoubtedly muscular in their nature. They arise at the line of junction of tbe sclerotic, cornea, and iris, and pass backwards, to bo connected to the ciliary pro- cesses. The name of Ciliary muscle is given to these fibres, 19. Immediately withm the cboroid, and extending as far for- wards as the ciliary processes, is the Retina, 20. This highly delicate and important moinbrane is formed partly of an espan- sion of the filaments of tbe optic nerve, 21, and partly of certain special structures which are peculiar to it. It occupies tbe pos- terior part of the globe. The surface, presented to the light, is concave. lis concavity is preserved by the peculiar structure called the vitreous body, to be afterwards described. It is per- fectly transparent daring life. Tiie optic nerve enters tbe eye- ball at tbe posterior part, not quite in tbe axis, but a little to tbe inner side. It passes through the sclerotic and choroid coals, and then its filaments separate from eacb other and divei^ in order to assist in forming the retina. Fig. 4 represents a view of the inner surface of the retina. 21 is the point of entrance of the optic Derve, from this the fibres all diverge towards the margin of the retina. The peculiar structures found in the retina are represented in Fig. 5, magnified many hundreds of times. These are extremely minute microscopic objects. Tbey are rod-like in their general shape, and may be called the rods of the retina. They are _ placed in the retina, with tbeir long axes forming almost a rig^ ^^^^Bgle with the long axes of the Qlaments of tbe optic DervOt^^^^J ^^^Hfn&eir inner ends, 22, look towax&B WeWf^V^^^ ^™ii^^^^l THE ETE-ltALL AND THE SENSE OP SIGHT. the narrow epacea between the filaments of the optic nervei Their outer ends, 23, are in close contact with the inner surface of the choroid coat. They present one or two dilatations ii their courae, which are probably somewhut like, in their atruc- ture, the cells in a nerve centre. Connected to one of these dilataliong, generally to the inni most one, is a Nerve Cell, 24. The connection being establiaheA' through the pole of the cell passing to the dilatation. Connected to another pule of the cell is a filament, 26, of the optic nerve. For all the filaments of this nerve must be considered as ter- minating through the mediuia of nerve cells in the rods of the retina. At one part of the retina, t. c, exactly in the axia of viraon, there are no optic nerve filaments ; only the rods exist- ing there. This spot, from its yellow colour, is called the Telli Spot, 26. Placed immediately behind the cornea is a chamber or cavil containing a watery fiuid, the Aqueous Humour, S Lying suspended in this chamber is the contraclile muscul curtain, the Iris, 28. The Iris is a circular, ring-like bod; attached by its circumference to the line of junction of the scler- otic and cornea. It is perforated in the centre by an aperture, the Pupil, 29. The iris contains involuntary mnacnlar fibres. Some of thi surround the margin of the pupil ; when they contract, diminish the size of the aperture. Their contraction takes pli whenever the pupil is exposed to a strong light, so that an cesaive quantity of light is prevented passing backwards to These changes in the iris take place involuntarily, and examples of reflex action. For the stimulus of eseesaive Ii being conducted to the brain by the optic nerve, is refiectef there through the agency of the nerve colls to the filaments of the motor nerve proceeding to the iris. These motor filanienls induce, in the muscular fibres of the iris, that contraction produces a diminDtion of the aperture at iVe ^m^. errej^^H rface ' IS in true- ^^^ inef^^^H »of ] k 178 THE EYE-BALL ASD THE SENSE OF StCT^. 1 The otiier fibres tire situated nearer the circDmrerence < iris i they have exactly the opposite action, for they filiate tfie pupil, so as to increase the size of the opening. Dilatation of the pupil takaa place when the light is feeble, and thus a greater number of rays are permitted to reach the retina. The muscularity of the iris is thus for the purpose of regulating the passage of the rays of light. The fluid in which it lies readily permitting its contractions to taie place. The colour of the iris varies in different eyes ; in Gome it is blue, in others grey, in others dark brown or hazel. It depends upon the presence of pigment, which, by rendering the iris opaque, prevents the transmission of rays of light through it. Directly behind the iris and pupil is the Crystalline Lena, 30. This is a double convex lens. The posterior surface is more convex than the anterior. It is a beautifully clear and trans- parent structure. It readily allows the rays of light to pass through, and it refracts them considerably in their passage. Prolouged for a short distance on to the front of the lens is a fine membrane which is connected behind to the ciliary processes, Through this connection the lens is brought under the action of the ciliary muscle in a manner which will be afterwards more fully explained. The back of the lens is lodged in a depression in the front of a delicate structure which, from its glass-like trans- parency, is called the Vitreous Body or Humour, 31. This fills up the great bulk of the posterior part of the globe. It gives to the retina its concave shape, for its outer surface is in contact with the inner surface of that membrane. The ciliary proeessK are lodged in depressions at its anterior part, as at 32 in tho fig. Passage of the Visual Bays, — From the explanation that hu now been given of Fig. 3, it will be seen that, situated in the axis of the eye-ball, are a number of transparent structures, through which the rays of light must all pass before they can h the retina. ffhese are (he cornea, aqueous bamti\w, M■^s\.■.^Si\UB Iwas, end THE EYE-BALL AND THE SENSE OF SIGHT. 179 vitreous body. Owing to the various degrees of convexity and density of these different media, the direction of the rays is con- siderably modified in their passage through them. By the aid of Fig. 6, this may be explained. Let A B repre- sent an object, from the extremities of which visual rays are emitted. These reach the cornea C, pass through it, and are refracted by it and the aqueous humour ; the refraction taking place towards the axis of the ray of light. The rays now enter the lens D, and are again refracted still more towards the centre ray. As they pass out of the lens into the vitreous humour E, they are again refracted, so that the rays finally meet at the points F and G, on the retina H, so as to produce at each of those spots a perfect image. The iris I, prevents rays passing through the circumference of the lens, which would be refracted differently from those proceeding through the centre ; the pig- ment, in its structure, absorbing all those rays which, by being transmitted through the outer part of the cornea, impinge upon it. The dilatation and contraction of this curtain permit, however, a greater or less number of rays to pass through the pupil, according to the vividness of the light or the condition of the eye itself. It will be observed, that the rays from the opposite extremities of the object cross each other ; so that the rays proceeding from the lower end pass to the upper part of the retina, those from the upper end to the lower part. Hence the image on the retina is inverted. This may be readily seen, by taking the fresh eye of a sheep, and removing the sclerotic and choroid coats from the back of the eye-ball, when the image of any bright object, held before the cornea, will be observed in the inverted position. The solution of the question, as to why images, which appear inverted on the retina, are yet perceived by the mind in the erect position, is one of the most difficult problems connected with the physiology of vision ; and it cannot be said, that any satisfactory explanation has been afforded of it. The per- fection o£ the image is owing to tbe d\SeretA. T«i^^ ^wsxnxi^^ \Rk ISO THE EYE-BAXL AND THE SESSE OF SIGHT, common poiot or focus on the retina. If tliey do not do tliis, bat converge either in front of or beiiind iLe retina, then iLe image is cuufuBeil and indistinct. Adaptation of the Eye to Distance. — As the bodies from wiiich the rajs of light proceed, are situated at varying distances from the retina ; and as the rays which proceed Irom iLem, strike the cornea at angles varying with tbe distance of tlie object, it is necessary that the eye-ball should be provided witb certain Btruetures, whicb may so afii^ct the varyiug angles of the visual rays, that they may all fall on the same focus in the retina. It is by means of these elractures, that tbe eye is enabled to adapt itself lo the vision of near and distant objects. There have been great diU'erences of opinion, at various times, amongst anatomists, as to the structures by which this adaptation is efTeiil^d. Some supposed that it 'waa due to a change in the convexity of the cornea ; others, lo the lens being muscular, and producing) by the contraction of its Gbre, changes in its curvature. The most recent investigations Into this subject Ebow, that, whenever the eye is adapted to view a near object, a change takes place in tbe curvature of the anterior surface of tbe lens, by which it becomes more convex. This is produced through tbe combined action of the iris and ciliary muscle. A necessary preliminary, is the contraction of the fibres that surround the margin of the pupil. This always takes place in looking closely at an object, so that the pupil becomes con- tracted. At the same lime, the fibres of the ciliary muscle con- tract, so OS to fix the ciliary processes and the point of attach- ment of the dilator fibres of the iris. By this means, the iris, which, Hinder ordinary conditions, is curved, becomes straighter, and thus presses upon the anterior surface of the margin of the lens, whicb lies directly behind it. Now, as the lens cannot b* pushed backwards, and as its substance is, to a certain extent, elastic, a change is produced in tbe curvature of the anterior sur/ace, which projects towards tbe pupillary apertur becowe more convex. M THE EYEBALL AJTD THE SENSE OF SIGHT. ^B^Vm experiment which proves this change in the^anlerior face of the lens to take plnce, is r very ingenious one. If n candle 19 held at some dislnnce from the cornea of a person, three images may be observed to be reflected from the trans- parent media of the eye — one from the cornea, a second from the anterior surface, the third from the posterior surface of tlie lens. If the candle is now brought much closer to the cornea, the second image is observed to move forwards, so as to come nearer to the first one. This can only be owing to the increase in the curvature of the anterior surface of the lens. The contraction of the iris, so as to produce a diminution in the size of the pupil, baa aheadj been mentioned as one of the I. necessary accompaniments of looking at a near object. The |1 contrary always occurs— namely, dilatation of the pupil — when a distant object is being looked at. This not merely allows the curvature of the lens to assume il^ former condition, but it also enables a much greater number of rays of light to fall upon the retina. ' Some individuals do not possess the power of adapting the I eye to diJTerent distances. Of these, some can only see distinctly objects placed at a considerable distance. These are long-sighted persons. Others, again, can only see distinctly objects placed very near to the eye : these are short-sighted. When a long- sighted person looks at a near object, the rays of light meet, not on the retina, hut behind it, so that a very indistinct image is produced. To remedy this, spectacles with convex glasses, must be employed ; for there the r.iys Trill be brought sooner to a focus, so that they will fall upon the retina, and thus produce a perfect image. When a short-sighted person looks at a distant object, the rays of light meet in front of the retina, instead of upon it. By the use of spectacles, with concave glasses, the con- vergence of the rays is prevented, until they reach the retina, 80 as to produce there a perfect image. Aotion of Light apon the Retina. — When rays of light Mi opon the retina, they induce nerve curtCTrta, 'w\i\'3tt.i '^■w% **^ 1 182 THE ErE-BALL AND THE SENSE OF SIOHT. ducted along, the filaments of the oplic nerve to tbe part d brain in which those filamcnlB terminate, induce there a eensa- tion of light. The rod-like bodies are the insti'umental media through which the external light produces the current. The connection of these bodies to the optic nerve filaments, through the intervention of the nerve cells, expluins the mode of paaaage of the current from the rod-like bodies to the nerve filamenla, which are simply to be regarded as conductors of nerve force, and perfectly incapable of being primarily excited by external light. This is proved by the circumstance, that, at the part of the retina where the optic nerve enters, and where there are only filaments of this nerve, vision is incapable of being induced. The j'ellow spot, which is the part of the retina in which visual impressions are most readily excited, contains do optic nerve filaments, but is formed exclusively of the rod-like bodies. The yellow spot is situated esactly in the axis of the eye, or the axis of vision ; so that it is the site of the most perfect vision. In looking at an object, slight movements of the eye-ball, through the agency of the muscles, are constantly going on, so as to bring the various parts of that object in succession into the axis of vision. It is probable that, to some extent at least, our ideas of the shape of an object are derived from the image on ihe retina cor- responding in its form to that of the object looked at. Our idea of size is also, it is probable, to some extent dependent upon the relative size of the retina brought under the influence of the rays of light proceeding from the object. In estimating, how- ever, both shape and size, we derive great assistance from the experience which has been afforded us by the education of the eye to the observation of different objects; for our ideas of the shape of a complex figure require that there should be something more than the imago of that ligure impressed on the retina. An efibrt of the mind ia necessary, ia order to determine the connec- lion tbat the various lines bear to each other, so as to obtain a JasC conception of their proper re\av\cmB. \^ "Ne cwi t»!i. \& tJhe THE EAB AND THE SENSE OP HEAEING. 183 sense of sight the assistance, at the same time, of touch, a much more clear and perfect idea is arrived at. The motion of an ohject is determined by the movement of its image over the surface of the retina, and also bj the move- ment of our own ejes which follow it. An impression made upon the retina by any luminous object, remains for a short period of time, even after the object has been taken away. The duration of this impression depends, to some extent, upon the brightness of the object, but more especi- ally on the length of time that the eye has been fixed upon it, and the degree of attention bestowed upon it. This is shown by the simple experiment, of twirling rapidly round a piece of lighted stick or string, when the impression produced upon any point of the retina remains until the object has reached the same point again, so that the idea of a luminous circle is conceived. CHAPTER XXm. THE EAB AND THE SENSE OF HEABIN6. The Ear is the organ placed at the side of the head to which the atmospheric vibrations that produce sound are transmitted, and in which certain changes are produced, which, when conducted along the auditory nerve, result in the perception of sound by the mind. Like the eye, the ear is a complex structure ; for there is to be considered, in connection with it, not merely the arrange- ment of the filaments of the Auditory nerve, but also certain accessory structures which assist in the transmission of auditory vibrations. Divisions of the Ear. — Anatomists are in the habit of dividing the ear into three parts — the outer, middle, and inner ear. The outer ear, called the Auricle, Fig. 9, 33, is placed on the exterior of the side of the head, \)eix\g la ^^'^^^ x^^v^i^ \si '^'^ hid^^^ 184 THE EAR AND THE BENSE OF HEABING. bone of the temple. It is composed of cartilage, over whidl akin is tiglitlj strewbed. The most depending part of the auri- cle, called Lobule, 34, does not contain any cartilage, butcoimsis of a fold of the skin encloiing fiit. The outer surface of the auricle preBents an irregular appear- ance owing to the preaence of several eleratioos and depressions. The most considerable of these depressions has opening into It a canal, which, if traced inn-ards, is found to CDtec the temporal bone. The canal is called the Externa! Auditory Meatus or Pas- sage, 35. It ia a little more than an inch in length. It is closed up at ila inner end by a tight membrane stretched across tti called the Membrane of the Tympanum, 3G. At the orifice of the canal, where it opens into the Kuricle, a number of hairs are always found growing. The skin is pro- longed down tlie passage, so ae to line it. If this part of the skin be examined, it is seen to present a number of small orifices, which lead into depressions in its sub- stance. These depressions are small glands, and in them is secreted that peculiar waxy matter called Cerumen, which is id- waya found in the auditory passage. If the ear wax is not re- moved by washing or other means, it is apt to collect in consider- able quantities. It then obslructa the ear passage, and is a frequent cauae of temporary deafness. The hairs at the entrance of the meatus and the peculiar accretion of its walls, prevent in- sects or other obnoxious objects from reaching the membrane (f the tympanum. Situated on the other side of the membrane of the tympanam is the cavity of the tympanum or drnm of the ear, constituting the Middle Ear, 37. This cavity is separated by the membrane from the external auditory paasage. It is a small bos-like space walled in on every side. It communicates, however, with the back of the nose through a long tube, the Eustachian Tube, 88, Along this tube air passes from the nasal passage into the tympanum ; the mucous membrane lining the nose is also pro- Jooged into it. A knowledge oS fcis tacV fMfeW \ja Ui e^'^lain THB EAB AND THE 8ENSE OF HEARING. 185 how it is that temporary and partial deafness is so oflen produced when a person suffers from a severe cold in the nose. The mem- brane becomes swollen, and prevents the proper passage of the air into the tympanic cavity. At the inner wall of the tympa- num are two openings in the bone, through which the tympanum would communicate with the internal ear if it were not that fine membranes are stretched across them. Situated within the tympanum are three small bones, which possess very peculiar shapes — Fig. 10, magnified several times. They are called the Hammer, 89 ; the Anvil, 40 ; and the Stir- rup, 41. They are articulated to each other by means of small joints. The hammer is connected by its handle to the mem- brane of the tympanum. The stirrup is connected by its broad end to the membrane filling up the oval opening in the inner wall of the tympanum that would have led into the vestibule. The anvil is connected on the one hand to the hammer, and on the other to the stirrup. These bones thus constitute a moveable chain stretching across the tympanum from the outer to the inner wall. Some small muscles are connected to them ; one of the most important of these is called the tightener of the tympanum, 42. This muscle is inserted into the handle of the hammer, and when it pulls upon it, it tightens the membrane of the tympanum.^^ The Inner Ear is a highly complex structure. From this cir-^ cumstance it is called the Labyrinth, 43. Both it and the tympa- num are situated in a very hard part of the temporal bone, which, from its almost stony hardness, is called the petrous portion of this bone. The Labyrinth is divided into three parts : the Vestibule, 44 ; Semicircular Canals, 45 ; and Cochlea, 46, Fig. 11. In this figure they have been considerably enlarged in order more clearly to represent them. The Vestibule is a very small cavity placed internal to the inner wall of the tjrmpanum, an oval opening existing in this wall, which is filled up by the membrane already described as having the base of the stirrup bone attached to it. The Semicircular Canals are three emaW <^\»cn^^ ^»2M)N& Q^\£^x^!^ THE EAR AND THE BEN8E OF HEAHlNfi. Into the back of the vestibule. A fine membraoe, coiTespoodiog exactly in shape to the vestibnle and the eanala, is contained in their interior. Within this membrane several small chalky de- posits, called otolithcs, 47, are found. The nerve of hearing, auditory nerve, sends a large branch to these parts, the termi- nations of the filumentfl becoming closely connected to these oto- litbes. Placed ivithin this membrane, and also lying between it and the bony cavities in whicli it lies, is a small quantity of fluid. The Cochlea ia placed in front of the vestibule. It is a small spiral canal in the bone, forming two and a half turns. It closely corresponds in its shape to the shell of the common snail. It is represented in Fig. 12, several times enlarged, with the outer wall removed, so as to show the interior. The canal of the cochlea is divided into two smaller canals by a thin spiral himina, 48, extending its whole length. These canals communicate with each other at the apex of iho cochlea, 49. At the base of the cochlea one of the canals opens into the front of the vestibule, so that the fluid in the vestibule becomes continuous with the fluid in the interior of the cocldea. The other canal would communicate with the tympanum by the round opening in its inner wall if it were not that a membrane stretched across prevented it. The spiral lumina of the cochlea posseaus groat importance, because upon it the filaments of the second division of the auditory nerve, 50, are distributed. These fila- ments are connected to bodies quite as peculiar in their structure as the rods already described in the retina. They differ JVom them, however, in shape and arrangement. They are called, after their discoverer, the rods of Corti. These peculiar rods are excited by the action of auditory vibrations, and, through th^ connection with the filaments of the nerve of hearing, cerl^ changes in the nerve force are induced in those filaments, wbicll, being conducted to the brain, produce the perception of sound. It must be remembered that the auditory nerve, like the optic, is a mere conductor of nerve force-, ani V\ia\,, vn utiit to induce THE EAB AND THE SENSE OP HEARING. 187 the currents along these nerves for the production of their spe- cial sensations by the natural stimulus, it is necessary that the induction take place through the peculiar structures connected with them. For the nerve of sight, the rods of the retina. For the nerve of hearing, the rods of Corti and their peculiar termi- nations in the vestibule. Function of the External Ear. — The peculiar shape of the auricle is for the purpose of collecting the atmospheric vibrations, and transmitting them along the external meatus which opens into it. The uses of this structure are especially shown in those animals who possess the power of erecting this part of the ear, and turning its cavity in the direction from which sound is proceed- ing in order more clearly to define it. The vibrations now pass down the external meatus, and impinge at the bottom of this canal upon the membrane of the tympanum. The walls of this passage abo exercise a considerable influence on the conduction of sound. Functions of the Tympanum. — ^The membrane of the tympa- num is by this means caused to vibrate, and the vibrations are propagated along the chain of bones to the oval membrane which separates the vestibule from the tympanum. These vibrations are permitted in the membrane owing to the compressibility of the air contained within the cavity of the tympanum allowing the necessarily small amount of movement to take place. Through the same cause also, the air by which the small bones are sur- rounded also permits their movements. The presence of air within the tympanum thus becomes a matter of very great importance, not merely by allowing the vibrations of the membrane and the chain of bones readily to take place, but also by producing an equalization of the pressure upon the inner as well as the outer surface of the membrane. The air enters the tympanum along the Eustachian tube, so that all animals that possess a tympanum also possess an Eustachian tube. If this tube becomes obstructed by any means, then the acuteness of hearing is considerably diminished. It has already been meDtioDed, that the hammer-sYia^^^ \^oxi^ ^\i\^ \^ ^^^- THE EAK AND THE SENSE OP nEABINO. 1 nted to the membrane of the tjmpanum, hne & mascle into it, the contraction of which produces tension of the branc. Espcrience shows, tlmt nil loud noisen, Boch aa Ik ^ report of a cannon, are eery disagreeable, and at timea eren painful. If the membrane of the tjmpannin is made very tight, the vibrations cannot be so readily cxci led in it, bo that soand is not so easily propagated to the Inbyi'inth, und its intensity it coDseqnenlly diminished. It is supposed that the tensor of tbs tympanum is put into action whenever the ear in exposed ta loud noises, so that by tightening the membrane it may aanst in lessening the intensity of the sound. FnnctiouB of the Labyrinth. — ^Through the agency of tin chain of bonos and the oval membrane, the Tibrations are pro- pagated to the oval membrane and the vestibule. They excit4 vibrations in the fluid of the vestibule and semicircular canals, which act upon the lerminations of the auditory nerves in tlis membrane lying in these two divisions of the labyrinth. At the same time, through the communication between the cochlea and tbe vestibule, the fiuid in the cochlea is caused to vibrate, wbieli, of course, influences the nerves distributed on its spiral lamina. In considering the action of vibrations upon the nerves in tho cochlea, it most be remembered that one of its small canals ia brought into relation with the tympanum through the membrane stretched across tbe round opening on its inner wall, Now, although the great majority of the vibrations of the membrane of the tympanum are directly propagated by the chain of bones W the vestibule, yet a few are, without doubt, communicated directly to the air within the cavity of the tympnnuro. These are transmitted across the cavity to the membrane filling np the round opening, which of necessity excites vibrations in the fluid of the cochlea. These must influence tlie nerves distributed upon its spiral lamina. Through the arrangements that have now been described, it will have been perceived that all the vibrations which afl^ct the oerre of bearing, impinge Upon it ihvou^ fcftTnftKvMn ^it ^.flnid. THE NOSE AND THE SENSE OF SMELL. 189 The tympanum, and the passage leading downwards t^ it, ^T^ not, however, the only channels along which auditory im- pressions may be conducted. The bones of the head are capable of doing this ; and the extremely dense nature of that portion of the temporal bone in which the labyrinth is situated, greatly fiicilitates the transmission of these impressions to it. It is extremely probable that the three divisions of the laby- rinth fulfil different purposes; that the vestibule has for its object the determination simply of sound, of mere noise ; the semicircular canals, again, determining the direction from which that sound proceeds. The cochlea, from the complexity of its structure, being the organ by which variations and degrees of sound are appreciated, as in the determination of musical notes or harmony. The varying power of appreciating music, in different persons, depending, perhaps, upon a more or less com- plete development of the peculiar structures with which the cochlear nerves are connected at their extremities. CHAPTER XXIV. THE NOSE AND THE SENSE OF SMELL. SrruATED within the cavity of the Nose are the two nerves called Olfactory, which convey to the brain the nerve currents which induce the sense of smell in the part in which they terminate. The nose is the prominent organ placed in front of the face, below and between the two eyes. It is placed above the mouth, and as it were guards that orifice, so that the odours of all sub- stances put into the mouth are perceived through its agency. In considering the anatomy of the nose, it must be remem- bered that it is a double organ, in the same sense as the eyes or ears are double. It is divided into two parts or nostrils, by a vertical partition called the septum o( \)[ie Xkiu^ ^\%. "V^^ "^^^ 190 THE KOSE AND THE SENSE OF SMELL. Each nostril is complete in itself. Each nostril opens in fro on the face, and behind into the pharynx. The anterior openings of the nostrils are surrounded by cart^i laginous plates, and the partition which separates one orifice frozn the other is also composed of cartilage. The outer wall of each nostril presents an irregular appearance, owing to the peculiar shape of the turbinated bones, which, as will be seen from Fig. 16, 52, are turned upon themselves. Between these bones are certain channels called the meatuses of the nose, 53. These meatuses communicate by orifices with the sinus in the frontal bone, 54, and with corresponding cavities in the interior of the ethmoid sphenoid bones and upper jaw bones. Into the lowest of the meatuses the tube leading downwards from the tear sac opens. The communications between the sinuses and the nasal cavity have induced some physiologists to suppose that they are sub- sidiary to the sense of smell. It is probable, however, that this is not the case, and that they are simply cavities in the bones of the head containing air, for the purpose of rendering them lighter than they would have been if they had been solid. The septum of the nose, 51, completely separates one nostril from the other. It is vertical in its direction, and extends from the roof of the nose to the floor. Its surfaces consequently con- stitute the inner wall of each nostril. The nose is lined throughout by a moist mucous membrane, which is prolonged through the openings in the meatuses into the cavities or sinuses existing in the above mentioned bones of the skull. This membrane is continuous posteriorly with the mucous membrane of the pharynx, whilst at the anterior nostril it be- comes continuous with the skin of the face. Beneath the mucous membrane in each nostril, both on the outer wall and also on the septum, the filaments of its own olfactory nerve are distributed, 55. These filaments do not extend beneath the entire substance of this membrane, but are confined in their distribution to the upper third of the nose. They are co/^nected to peculiar Bltuelxxx^ft \Ai\Oa. ^^^^^t to cor- THE NOSE AND THE SENSE OF SMELL. 191 respond to the rods already described in connection with the extremities of the optic and auditory nerves ; for by their agency are induced, in the olfactory nerve filaments, those currents which produce, in the part of the brain in which they terminate, the sense of smell. The sense of smell is excited by odorous emanations from sub- stances which, suspended in the atmosphere, enter the nostril, and there influence the olfeictory nerves. One condition most essential to the excitation of this sense is, that the odorous par- ticles should be capable of being dissolved in the mucus secreted by the membrane of the nose. It is owing to this circumstance that the sense of smell is always either impaired or temporarily lost in a person suffering from an attack of catarrh or common cold. In the first stage of this affection, the membrane is dry, owing to its secretion being no longer formed, so that the odorous exhalations are incapable of being dissolved. In the subsequent stage, the cavity of the nose becomes filled with the abundant secretion of the membrane, so that the odorous particles never reach it. The intensity of this sense is heightened by making rapid and frequent inspirations through the nose, so as to bring successive portions of these particles into relation with the filaments of the olfactory nerve. The limitation of the distribution of the nerve to the upper part of the nose ensures a certain amount of warmth being communicated to the inspired air before it reaches the fila- ments, a circumstance which appears to facilitate the induction of the sense of smell. GENERAL RELATIONS OF THE SENSES. The various senses that have now been described, vary in intensity very much in different persons. This appears to a great extent to depend upon the degree in which any particular sense has been cultivated. The habit and modes of life of the individual thus influence materiaUy t\i^ ^^^^fe qI ^^^'l^yslw^^'^ l' cerlain sounds, which we are in the habit of ri ' !!r-il!v ?.- ■'-.■ -■:.' ,-,r letters. According as oi : vutoa in the formation of c ,1 ^«nting them spoken of by tl 'L;Li, 1^ .labial. lagrecable afi'ection called stai t majority of instances, upon t Jesercise perfect control aver ■n the proiMcftoTi «K s^esi^- 198 CONCLUSION. always much worse when the person is labouring under any great emotion, because then the very slight control which, in tranquil moments even, he is enabled to place upon these muscles, becomes considerably diminished. Hence, in the treatment of this affection, the speech should be slow and • deliberate ; the mind, as much as possible, should be led away from the contem- plation of the disorder; and especial care should be taken to avoid all mental emotion at the time of speaking. The sense of hearing appears to exercise a great influence upon the production, not merely of the voice, but of those sounds by which speech is effected. A person with a quick and ready ear, and whose speech organs are properly formed, will much more readily acquire the power of forming a new sound, such as he may meet with in the acquisition of a foreign language, than one whose sense of hearing is not so acute or precise. Hence it happens that persons who are bom deaf are at the same time dumb ; for, as they have never heard the sound of any language, it is not possible that they can imitate them. CHAPTER XXVI. CONCLUSION. In the preceding pages, a sketch has been given of those struc- tures and functions which minister to the growth and main- tenance of the life of the individual, by which he increases in size, as in the passage from the state of infancy to that of adult life, and by which, after having arrived at the latter stage, his system is preserved in a condition adapted to the performance of its various duties. Those processes, the office of which is to assist in the reproduction and perpetuation of the species, will not here be considered. It will have been seen, that for lYi^ p^ifotm«xkfift of the numer- CONCLUSION. 1 99 ous functions different organs are set apart and peculiarly adapted, each fulfilling its own office in a highly perfect manner. One of the most essential characters by which man and the higher animals are distinguished from the lower types of orga- nization, consists in this differentiation of the organs, as it has been termed ; that is, the setting apart of particular organs for particular purposes. In the very lowest forms of life, the separation of the body into different organs does not occur. The whole substance of the animal appearing indifferently to perform the various func- tions required of it. But whilst we observe the differentiation of organ and function in those higher types of organization repre- sented by man and the animals most closely allied to him, we must not forget that the different parts are mutually dependent upon each other. Hence it happens, that when disease or injury impairs the structure or functions of any particular part, the whole system, to a certain extent, suffers ; this being dependent upon the amount of injury that the organ has received, or its im- portance in the economy of the individual. Many of the organs most closely related to each other in their function appear to possess, however, a curious compensating influence, by which an impairment of the function of one is follow^ed by an increase in the activity of the other. This is especially shown in the case of the skin, lungs, and kidneys. All these organs possess, as one of their functions, the power of excreting or separating water from the system. It has been found by observation, that when this is interfered with in one of these localities, the others put on an increased action. The duplicity of many of the organs is evidently for the purpose of enabling the functions performed by them to be carried on, should one be seriously injured. That this is the case, is shown by the circumstance, that if one is destroyed, an increase takes place in the size of the other. Over all the organs the nervous system exercises a controlling influ- ence, so that it must be ranked as amongst the most important of them all. 200 CONCLUSION. In contemplating the adaptation of the different organs to the functions they are destined to perform, one cannot fail to admire the abundant indications of Design exhibited in the construction of the different parts ; how they are all brought to bear upon one common end, viz., the preservation of the body in a state of health ; and how, for this purpose, the mechanism and mode of action of each part is perfect in its nature. But whilst there exists in the Economy a power by which it can renovate itself, so as to make good the waste that is con- stantly taking place in it in the exercise of its functions, yet there is a natural tendency in the tissues or organs to degenerate or decay after the lapse of some time. The period at which this may take place appears to vary greatly in different individuals, and to be, to a great degree, dependent upon the conditions by which the individual is surrounded. This degeneration may manifest itself in various ways, but especially in the two follow- ing : — ^The deposition of fat in certain organs, or parts of organs, so that the natural structure of the part becomes replaced by fatty materials. The withering or drying up of the parts, so that they become wasted and shrivelled ; this form is generally seen in old persons. In addition to the tendency to degeneration, which may be considered natural to the body, it suffers at various times from attacks of disease. These may be produced by the neglect of the individual, who, indulging in excess or errors of diet, or subject- ing himself to noxious emanations, or failing to attend to personal cleanliness, induces disease in those parts of his body which are especially exposed to these different injurious influences. Numbers, however, of diseases appear to be produced, not so much by the neglect of individuals, as by communities failing entirely to look after the means of preserving health, or doing so in an inefficient manner. The crowding together of numbers of persons in con- fined localities, without providing methods by which the various emanations and excretions proceeding from them may be cleared ^waj-, is one of the most fruil?u\ pTftd\a^oavcv^ ^^\jl^^"& c^C disease; CONCLUSION. 201 especially of those epidemic disorders, which, raging like pesti- lences, carry dismay and death into numerous households. That emanations from animal bodies are injurious to the health of other animals, appears to be a fact, about which, at this pre- sent time, there cannot be a doubt. The earth and the atmos- phere are the great receptacles naturally provided for the diffu- sion and dispersion of these various disease-inducing influences. But whilst they exercise deleterious effects upon animal life, they are of the greatest value in promoting the growth and nutrition of plants, the food of which consists of those materials, that not merely cannot minister to, but absolutely produce an injurious influence upon the life of animals. The two great divisions of the organized world thus bear a very curious relation to each other. The animal evolves certain materials, which, either conveyed by the air or commingled with the soil, reach the plant, and are by it applied to the purpose of its nutrition. Through these means the plapt developes and grows, and prepares those mate- rials which, when taken as food by the animal, after digestion and absorption, can be applied to the nutrition of its tissues. THE END. MUBRAY AND QIBB, PB.VN't!&1l&« ILDV^'^T^B.V^^. I